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Climate change impacts: case studies

Climate change impacts: case studies

Climate change is not just about data and trends – it has major consequences for the well-being of people and the planet.

In its most recent report on impacts and adaptation, the IPCC states that human-induced climate change “has caused widespread adverse impacts and related losses and damages to nature and people, beyond natural climate variability.” Some of those impacts are happening slowly and ‘behind the scenes’ as long-term trends in temperatures and precipitation, or other climate variables. We also witness them in ecosystem changes, when plants and animals shift habitats or even disappear. 

Other impacts come in the form of extreme weather events, which scientists are able to link or attribute to climate change. Extremes such as cold spells, torrential rains or heat waves, which are fairly unlikely but can have profound consequences, have always been part of the natural climate variability. Through our influence on the climate system, however, humans are ‘putting our finger on the scale’, with these events becoming more likely and their consequences increasingly more severe. The IPCC reports refer to this as ‘beyond natural climate variability’.

Thanks to human ingenuity and resilience, many communities have found ways to adapt to both acute and more long-term climate impacts, minimising the devastation they cause. Yet, some impacts are simply impossible to adapt to and the losses they cause are often irreversible. As we delay meaningful action on reducing greenhouse gas emissions, we are losing ground on adaptation as well. This is in part due to the fact that time is running out for some of the solutions that could have worked earlier at lower levels of warming. It is also due to growing costs as well as depleting adaptive capacity, wherein living beings and communities that are struck by multiple or overly frequent impacts lose the ability to recover.

In this deep dive, we will look at recent examples of extreme heat, flooding and drought for which climate scientists working for the World Weather Attribution (WWA) project have been able to identify and quantify the link to climate change.

Land and oceans under extreme heat

Alisdare Hickson / Flickr

In the spring and summer of 2022, abnormally high temperatures hit multiple regions of the world. First, India and Pakistan as well as large parts of South Asia experienced a heat wave that was about 30 times more likely because of climate change, according to WWA estimates. Scientists note that while heat waves are not unusual before the monsoon, the combination of extreme heat and much less than average rain led to disastrous consequences for public health and agriculture. These impacts were compounded by other non-climate risks, such as a shortage of coal leading to power outages in India. They also had far-reaching implications for the rest of the world, as reduced wheat crop yields prevented the region from supplementing the global supply hit by the war in Ukraine.

Later in 2022, summer heat waves in Europe caused major disruption in people’s lives and economic activity. In France, exceptional heat interfered with electricity production from nuclear power plants, while the United Kingdom logged its first ever temperature above 40°C. An analysis from WWA concluded that, without human-caused climate change, that would have been extremely unlikely.

Extreme heat can be just as dangerous when it happens in the ocean as it is on land. Prolonged periods of abnormally high surface water temperatures are called marine heat waves, and their frequency and intensity have increased due to climate change by more than twentyfold, according to a 2020 study. This study also showed that, of the seven highest-impact marine heat waves since 1981, all but one could be tied to human-driven warming.

Flooding: extreme rain and tropical storms

Bärwinkel,Klaus, CC BY-SA 4.0

In January and February 2022, Madagascar, Mozambique, Malawi and Zimbabwe experienced a series of tropical storms, including three that were strong enough to qualify as tropical cyclones. These storms brought deaths and injuries as well as vast infrastructure damage, and their long-term consequences for the well-being of highly vulnerable local communities are yet to be fully understood. The WWA team was able to show that climate change increased the likelihood and intensity of the rainfall associated with two of the storms, Tropical Storm Ana and Tropical Cyclone Batsirai.

In 2021, two days of very heavy rainfall compounded by wet weather conditions beforehand and other local factors caused severe flooding in Germany and parts of Western Europe. Over two hundred people lost their lives, and hundreds if not thousands more faced damage to their housing and transport infrastructure, or were temporarily cut off from evacuation and emergency response. While it is difficult to detect local trends in precipitation and make conclusions on how much more likely climate change can make these events, the WWA study established that an upward trend is evident for the larger region of Western Europe.

Drought and water shortages

Too little precipitation due to drought can be just as devastating as storms and floods. In the summer of 2022, water shortages, fires and crop losses across the Northern Hemisphere were driven both by the high temperatures mentioned above and exceptionally low rainfall, with soils drying out particularly in Europe and mainland China. The WWA analysis established the cause to be related to the higher than average temperatures rather than the lower precipitation, meaning that our agriculture and energy systems are more likely to face these ‘one-two punches’ of combined risks as the climate warms.

Useful resources

Understanding carbon dioxide removal

Understanding carbon dioxide removal

To prevent dangerous warming, we need rapid and deep emissions cuts. But having delayed action for decades, reducing emissions may no longer be enough.

How we address climate change as a global problem depends both on our choices in policy and economic development and on the physical constraints of the climate system, notably the greenhouse effect itself. As long as we continue to emit carbon dioxide and other greenhouse gases into the atmosphere, we’re putting more pressure on the climate while the list of options for policy choices gets shorter. As we discussed in the [explainer on carbon budgets] (link to the carbon budgets deep dive), there is only so much we can emit before we breach the safety limits on temperature rise. And if we ‘overspend’, current and future generations may face the bill in the form of [various climate impacts] (link to the case studies deep dive).

The underlying physics of this problem we face also presents potential solutions – in other words, if putting CO2 into the atmosphere from power plants or transport can heat up the Earth, then taking it out can compensate and limit, or even reverse temperature rise. This is the idea behind carbon dioxide removal (CDR) technologies, which are now, after years of insufficient progress on climate change, being increasingly discussed as a potential solution.

Today, CDR underlies many ‘net zero’ plans and pledges, where some greenhouse gas emissions that have already happened or will happen in the future are ‘cancelled out’ by removals, often happening somewhere other than the emitter’s location. It is also used in the so-called overshoot scenarios, where the Paris Agreement temperature goals are temporarily broken because we don’t reduce emissions fast enough. In these cases, CDR helps us get back into the ‘safe zone’ later this century, turning our total CO2 emissions negative by taking out more CO2 than we emit.

Can you really pull CO2 out of the atmosphere?

Adam Cohn

CO2 extraction is possible and has, in a way, always been happening. There are various kinds of CDR being discussed now, depending on what chemical mechanisms are used to capture the greenhouse gas in question, and how the captured carbon is then stored. One of the mechanisms is photosynthesis, the natural process in which plants and some bacteria convert water, light energy and carbon dioxide into chemical energy, releasing oxygen in the process. Photosynthesis is the reason why the Earth’s atmosphere has enough oxygen to support complex life forms like humans. It is also the means by which living organisms capture and store more than half of all CO2 emissions from current human activity, making them carbon sinks.

Scientists have been accounting for these natural carbon sinks in their modelling. For photosynthesis to count as a proper CDR method, however, it has to be intentional and additional to what nature is doing on its own. In other words, we can’t simply think of all plants on Earth as one giant CDR project and rely on it. Instead, people can intentionally plant and maintain forests on land or in coastal areas, enrich soils, or grow some plants used to produce biofuel (and then capture the CO2 from burning it).

Furthermore, if plants can use chemistry to capture CO2, then people can also use chemistry to do this. For example, if certain solvents or sorbents are exposed to open air, they will bind to CO2 and absorb it, a bit like a sponge absorbs water. And, like a sponge, the CO2 can then be separated out and the initial chemicals reused. This process is called direct air capture (DAC), and the resulting CO2 is stored somewhere to make sure it is completely removed and not re-emitted to the atmosphere. There are solid and liquid materials that can be used for DAC, as well as some less developed innovative methods of scrubbing CO2 from the air.

Weathering, or gradual deterioration of rocks and minerals in contact with air, water or living organisms, is another natural process that already impacts the world around us and which we can intentionally make use of to counter climate change. Some chemical mechanisms of weathering involve CO2 from the atmosphere, and this itself can be purposefully enhanced to speed up reactions, for example, by spreading finely ground basalt on surfaces. As with plants, however, it counts as CDR only if it is intentional and the CO2 is successfully captured.

Can CDR solve our climate problem?

Even though the fundamental chemistry of various kinds of CDR looks solid on paper, making it a reality has been a challenge so far. The chemical processes of direct air capture and enhanced weathering can be energy-intensive and not very efficient. Currently, CO2 captured via these methods costs so much that it makes little economic sense to pursue these projects. Part of the reason for this is that, unlike renewable energy, these technologies are still in their infancy.

In the case of biological CDR, plants have been perfecting photosynthesis for millions of years, making that natural ‘technology’ fairly mature. But biological CDR using forests planted by humans can have significant impacts on food security, biodiversity and land rights. Furthermore, while it is less expensive than chemical CDR, the current size of our influence on the climate makes it impossible for biological CDR to compensate alone. Once again, the physical constraints are at play here: for our current level of greenhouse gas emissions, there simply is not enough land on Earth. And, of course, carbon removal by plants would not be permanent or even long-term if the trees and plants used are not carefully protected from fires or logging.

If CDR is going to be used to cover our collective ‘overspending’ of the carbon budget, there needs to be proof that enough CO2 would actually be permanently removed from the atmosphere. This would itself require reliable methods for measuring the CO2, reporting the information and then verifying the results, none of which are yet in place.

Overall, counting on CDR to solve our climate problem would be like placing a risky bet on a future outcome that is still only vague. These technological solutions are simply not certain to mature in time to prevent us from causing temperature overshoot. If we decide on policies today that rely on them and they do not work in the way we need, we will have missed the opportunity we have now to stop emissions from getting into the atmosphere in the first place – and there will be no going back in time to choose differently.

What can CDR do then?

The IPCC states that CDR can help us counterbalance so-called ‘hard-to-abate’ residual emissions from things like aviation or heavy industrial processes. Total decarbonisation in these sectors can be either prohibitively expensive or take too long because the necessary technologies are not yet available at scale. To help avoid the climate impacts from emissions in these areas, CDR can be used to compensate for their activities by removing CO2 from the atmosphere.

Carbon removal in the next few decades is likely to be limited and nowhere near capable of dealing with the amount of emissions that need to be accounted for each year to avoid exceeding the limits of warming. As such, the IPCC indicates that the limited capacity of CDR should cover only hard-to-abate sectors and cannot serve as a ‘get-out-of-jail-free’ card for everything else. The latest IPCC report actually reduced the role of CDR in its proposed economic pathways compared to its earlier scenarios for meeting the Paris Agreement goals. The message is clear: reducing emissions should be the focus of our actions.

Useful resources

  • At an event during COP27 in Egypt, IPCC authors speak about CDR and how it is featured in the Working Group 3 report
  • The first of its kind State of Carbon Dioxide Removal Report, released in early 2023, looks at the state of CDR globally
  • A glossary of CDR terminology from the American University
  • Another explainer on how CDR works from the American University

What is a carbon budget?

What is a carbon budget?

Science can outline the dangerous consequences of various levels of warming for humans and other life on Earth, but these are possible destinations and not roadmaps.

The goals of the 2015 Paris Agreement are based on the implications of what 1.5°C and 2°C of warming would mean for humans and other species. They set the relatively ‘safe’ boundaries within which some irreversible but not catastrophic damage will occur. The IPCC reports and other research show that limiting the global average temperature rise this century to well below 2°C will mean we can avoid the most dangerous consequences of climate change. If we do, there is also hope of adapting and building a resilient and more sustainable future.

Yet there is no thermostat for the whole Earth into which we can easily dial these numbers. The temperature goals alone are not enough to guide climate change policy because the level of warming we achieve will depend on a complex range of decisions made over time by governments and businesses around the world. This national, regional and local decision-making will be effective in setting policy targets and creating incentives for change through governing greenhouse gas (GHG) emissions rather than temperature.

To translate temperature into emissions and make the Paris goals actionable, scientists use so-called carbon budgets. In some ways, they work just like a financial budget: there is a cap on total spend – the amount of greenhouse gases we can emit, and this ensures we stay within the ‘safe zone’ and avoid going into debt – to future generations in this case. But carbon budgets are also quite different. A look at your financial accounts and income streams is usually enough to judge personal spending limits, whereas in a carbon budget scientists must also calculate the total amount of greenhouse gas emissions compatible with various levels of warming.

With these calculations included, carbon budgets can show us several things: how we are actually doing (the historical budget), how much more time we can keep ‘spending’ at current levels (the remaining budget) and what a fair and equitable allocation would look like when sharing the total budget between countries.

How do carbon budgets work?

In your own budget, the final figure – how much money you have available without needing to worry about overspending – is only possible with details of your income and costs. Similarly, a carbon budget starts with scientists identifying the sources of carbon coming into the atmosphere and the sinks capturing carbon from it (such as forests or the ocean). Advances in climate and earth sciences mean it is possible to build a balance of the carbon cycle in nature and then add an additional source: emissions from human activity.

In a personal financial budget it can be important not to drop below zero to avoid being unable to pay for something or resorting to costly loans. In the climate system, the amount of carbon in the atmosphere – measured as a concentration in ‘parts per million’ (ppm), creates the ‘greenhouse effect’ and gives the level of global average temperature. It is this temperature level we are concerned about, since exceeding the Paris Agreement’s 2°C limit would bring consequences that countries have agreed are unacceptable.

To balance your own budget, you can cut some costs, try to earn more, or get a loan and dip into your future income to repay the loan with interest. To balance a carbon budget, we can also ‘cut costs’ by figuring out how to adapt to the consequences of global warming, but the options are quite limited – we can’t negotiate with the Greenland ice cap for a reduction in climate change-driven melting, for instance. ‘Earning more’ for a carbon budget means deep emissions reductions through things like renewable energy and energy efficiency and other measures. And ‘getting a loan’ means transferring responsibility to future generations that would have to act more aggressively – not just to reduce emissions but to bring them to negative levels by successfully capturing more greenhouse gases than are emitted.

Lastly, a financial budget may have income and spending in various currencies – as it is not possible to add and subtract these different currency units directly, we convert them to a common currency for comparison. Likewise, budgets are calculated for each of the greenhouse gases in the atmosphere and then made comparable by ‘converting’ them into units of carbon dioxide equivalent (CO2e) – carbon dioxide is used since it is the dominant greenhouse gas emitted from human activity.

Matjaz Krivic / Climate Visuals Countdown

So what’s our carbon budget?

The most well-known exercise in tracking our carbon budget comes from the Global Carbon Project – an international research project within the Future Earth research initiative on global sustainability, and a research partner of the World Climate Research Programme. In 2022, more than 100 researchers got together to build the 17th edition of the budget for CO2.

Firstly, the Global Carbon Project’s budget describes trends in global emissions of CO2 from energy and land use. For instance, in 2022 fossil carbon emissions continued to rise and reached 36.6 billion tonnes of CO2 – 1.0% above the year before. This rise was slightly more than the previous pre-pandemic peak in 2019 and is far from what is needed to reach the Paris Agreement goals. Instead, a rapid decrease at the scale of about 1.4 GtCO2 each year is required to reach net zero CO2 emissions by 2050.

The global carbon budget also tells us how much we are able to emit and still stay on track for 1.5°C, 1.7°C or 2°C of warming – that is, 380, 730 and 1,230 billion tonnes of CO2, respectively. To make these figures less abstract, scientists usually present them as years of ‘doing the same thing we were doing last year’. Based on 2022 emissions levels, we have nine more years until we breach the 1.5°C limit, and just 18 and 30 more years before we exceed the higher boundaries.

Useful resources

  • The Carbon Budget for Dummies, an explainer from one of the Global Carbon Project researchers at CICERO.
  • An even deeper dive into carbon budgets from the World Economic Forum.
  • The MCC Carbon Clock, which visualises the carbon budget as a countdown, showing how much CO2 can be released into the atmosphere until the safety limits are hit.
  • A three-minute video explainer on carbon budgets from the Carbon Tracker Initiative.

Food and climate change

Food and climate change

The global food system – from fields and farms to our dinner tables and waste bins – provides livelihoods for over 1 billion people.

The 2019 IPCC report on Climate Change and Land states that food supply per capita has increased more than 30% since 1961, with the food system overall producing more than enough calories to feed the world. Latest UN data suggests however that as many as 828 million people were still affected by hunger in 2021, with an estimated 45 million children under the age of five suffering from wasting: the deadliest form of malnutrition.

Our current food system, already under immense and growing pressure from conflicts, economic shocks and deepening inequality, is also threatened by climate change. For example, according to the most recent IPCC conclusions on impacts and adaptation, climate change has already dampened productivity growth and decreased fish stocks. Since we rely on a handful of crops dominated by a few companies, international commodity shortages and price spikes are increasingly likely in a highly interconnected and less resilient system. Further warming, driven by current and future greenhouse gas emissions, is projected to cause declines in crop production and to render major parts of the world unsuitable for existing agricultural models.

The IPCC report projects that the number of people at risk of hunger by 2050 will increase by between 8 and 80 million depending on the level of warming. Those most impacted will be people in Sub-Saharan Africa, South Asia and Central America. Small and mid-sized food producers in these regions play a key role in global food security, as rural households in low- and middle-income countries produce half of the world’s cereals and the majority of fruits and vegetables. However, they already lack the resources to cover their losses from droughts and other climate-related events – which are projected to be worsened by climate change, or to adapt to harsher conditions.

Additionally, if greenhouse gas emissions stay high, up to 30% of current crop and livestock areas will become unsuitable for food production by the end of the century, according to the report. Conversely, if we reduce emissions rapidly, we will lose less than 8% of that agricultural land. In this respect, South Asia, South East Asia, parts of Australia, the Sahel region in Africa and the area around the Amazon basin in South America are the most vulnerable regions.

It is not possible for us to simply adapt to these adverse changes when they happen, or prevent them from happening through present adaptation measures. But cutting emissions along with diversifying food production systems and supply chains will reduce these risks – through increased resilience in global food systems and lower exposure to extreme weather events.

Furthermore, transitioning to greener, more climate-friendly food systems on both supply and demand sides will in itself reduce warming: the UN Food and Agriculture Organization (FAO) estimates that, by 2021, the world’s food systems were responsible for more than one-third of global greenhouse gas emissions from human activity.

What will happen to staple crops?

Dhana Kencana / Climate Visuals

Crop yields have increased over the last six decades, but climate change has already shaved off about 21% of that growth through various impacts like higher temperatures, more frequent and powerful extreme weather events, and changes in pest populations and soil degradation. In this century, the yield growth trend could even reverse by up to 3.3% per decade for crops such as maize, soybean, rice and wheat, depending on location and specific crop variety. And while more carbon dioxide in the atmosphere could potentially boost crops, this will not compensate for this effect’s flip side: increased CO2 levels also reduce the levels of nutrients and vitamins in crops, which makes them less nutritious and can affect pollination and reproduction.

Human-induced warming will exacerbate the risks of simultaneous production failures of key crops in major countries, triggering a domino effect in the food system. Crop yields in different areas of the world are connected via large-scale climate patterns (for example, El Niño and La Niña, or the warming and cooling phases of the periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean). Changes in these patterns driven by climate change may affect crops across the world at the same time.In fact, there is evidence that the risk for simultaneous crop failures has already increased for wheat, soybean and maize compared to 1967-1990. These risks are projected to increase dramatically with further warming, along with the potential for global disruptions in food supply. Climate change also poses the risk of more frequent individual extreme weather events across the world, creating a potential ‘perfect storm’ in food supply chains.

If the global average temperature rises by more than 2°C, then adaptation alone will be insufficient to prevent climate change from reducing crop yields, no matter how much money is invested in adaptation measures. That said, adaptation is indeed necessary, and the costs of it combined with the cost of losses from warming are projected to increase from $63 billion for 1.5°C of warming to $128 billion for 3°C of warming. But there are solutions for cutting this bill. In addition to rapid emissions reductions across sectors, industrial agriculture – which is energy- and water-intensive, fertiliser-heavy and based on monocultures – can be, and will need to be, transformed to take a more diversified and sustainable approach.

How will animal husbandry work?

Robert Benson / Aurora Photos

Large-scale industrial cattle and poultry farming is a significant contributor to human-induced climate change, due to both greenhouse gas emissions from animal farms and extensive land use for feed production. Raising cattle often requires pastures created by clearing woodland, which makes the resulting meat and dairy products especially emission-intensive – the cleared trees no longer capture carbon and instead release previously stored carbon into the atmosphere. Cow digestion also produces methane, a more potent greenhouse gas than CO2, while growing animal feed adds to nitrous oxide emissions from fertiliser use. Taking another perspective, human-induced warming also causes harm to farm animals, as high temperatures affect their health, growth and production.

The IPCC reports offer several ways to address this problem. On the supply side, better management of lands used for grazing, improved handling of animal manure and higher-quality feed can all make livestock rearing and food production less carbon-intensive, reducing its contribution to human-induced climate change. But, ultimately, demand must shift to healthier and more sustainable diets, particularly in developed countries, with more protein coming from plants and seafood rather than from meat.

What about fishing and seafood?

Shibasish Saha / Climate Visuals

Climate change affects the ocean in multiple ways, from the more well-known rising surface temperatures, acidification and sea-level rise to algal blooms and low oxygen levels, parasite spread, marine heat waves and other extreme weather events. Due to the impacts of climate change that we are already experiencing, global yields of fisheries decreased by 4.1% between 1930 and 2010, with some regions seeing losses of 15% to 35%. Marine heat waves in particular, having already caused collapses of local fisheries and aquaculture, are projected to become 20 to 50 times more frequent by the end of the century.

Fish populations are disrupted by profound changes in their habitat. This can interfere with established fishing routes and affect potential seafood catch in tropical regions, adding to already unsustainable practices that include extensive overfishing and the use of plastic nets – these and other discarded, or ‘ghost,’ fishing gear are the deadliest source of ocean pollution. Again, taking another perspective, aquaculture, or ‘farming in water,’ is an increasingly important source of fish, seafood and seaweeds and is also harmed by the impacts of climate impacts.

Useful resources

  • Food and Agriculture Organization of the United Nations (FAO) presents its 2022 State of Food Security and Nutrition in the World in a five-minute video.
  • Environmental impacts of food production from Our World in Data.
  • A 24-minute episode of Radio Davos, a podcast from the World Economic Forum, titled ‘COP26: Feed the world without destroying the climate’.

Climate change and biodiversity

Climate change and biodiversity

Climate change and biodiversity loss are two of the most important challenges we face, and these interconnect in many ways.

Even though life on Earth has always been evolving in a changing climate, the relative stability over recent millennia has provided favourable conditions for both wildlife and human civilisations. Many plants and animals have adapted to specific temperatures or water availability. But with those now changing due to rapid warming, many species will not be able to adapt in time. Some species, especially those in polar and mountain regions, have nowhere to escape the rising temperatures and so face extinction. Moreover, altered climate signals like the early onset of spring interfere with seasonal activities, such as blooming or mating, with these disruptions having knock-on effects in the food chain and ecosystems.

Wildfires, heat waves and other extreme weather events devastate entire ecosystems, both on land and in the ocean. Recovering from these one-off events, which are growing in intensity and frequency, is also more and more difficult. The stress induced by climate change, both acute and chronic, only further exacerbates other risks – for example, from cutting down forests, or air, water and soil pollution, excessive hunting and fishing, or the spread of invasive species, and so on.

Additionally, nature has always been crucial in relieving the pressure caused by humans on the global climate. More than half of all CO2 emissions from our activity is captured by plants through photosynthesis and temporarily stored in living and dead biomass, or dissolved in the ocean. Living organisms also affect the physical parameters of the climate system, such as land surface reflectivity and the formation of clouds and dust in the atmosphere. 

Healthy and diverse ecosystems therefore can help humans survive climate impacts such as extreme weather – for instance, intact forests retain rainwater and reduce damage from flooding, whereas coastal wetlands prevent erosion and flooding from sea-level rise. Ecosystems can also help us adapt to the changing climate, supporting livelihoods and creating sustainable food and energy solutions for local communities.

Important though it is, protecting biodiversity from climate change is not just about preserving beautiful living things for their own sake. Coral reefs, threatened by more frequent marine heat waves, support lots of fishing livelihoods. Forests hold economic and cultural value for countless local communities. Furthermore, as ongoing warming and environmental degradation erode the carbon-storing capacity of natural ecosystems, there is a significant and increasing risk of feedback loops, making an already bad situation worse.

The IPCC and IPBES (the Intergovernmental Platform on Biodiversity and Ecosystem Services), have concluded that biodiversity loss and climate change are inseparable threats to humanity that must be addressed together. If we fail to do so, we risk irreversible losses and damages. But, on the other hand, success will mean additional benefits for our health and quality of life.

What does projected warming mean for biodiversity?

The 2022 IPCC Working Group II report on impacts and adaptation goes into great detail on what would happen to plants, animals and whole ecosystems in different scenarios of warming. For example, marine and coastal ecosystems, such as kelp forests or seagrass meadows, will be irreversibly damaged or destroyed if temperature rise exceeds the 1.5°C threshold. Coral reefs alone face a decline of 70-90% at this level of warming, while at 2°C the decline is projected to reach 99%. Conservation efforts for most coral reefs will have little success past 1.5°C of warming. Beyond average temperature increase, ocean and coastal ecosystems are also threatened by marine heat waves, which are projected to become 20 times more frequent even if warming is limited to 2°C. 

Dhana Kencana / Climate Visuals

The combination of various stresses from climate change and other environmental pressures will likely drive extinctions of plant and animal species at least 1,000 times faster than the natural rate, both on land and in the ocean. But this is not yet locked in, as cutting greenhouse gas emissions and changing our climate trajectory will greatly reduce the extinction rate.

Beyond the extinction of individual species, climate change can and will trigger fundamental and irreversible changes in ecosystems. This will, in turn, affect local weather and accelerate climate change. We are already observing biome shifts, for example, from rainforest to savanna. These shifts are projected to happen on less than 15% of land if temperature rise is less than 2°C, but if we miss this target and temperature rise is closer to 4°C, these shifts will happen on more than a third of the Earth’s land surface. Environmental changes of this magnitude will have profound knock-on effects for human livelihoods and well-being, as well as on biodiversity.

What do various solutions mean for biodiversity?

The IPCC report concludes that, as global average temperature rises, conservation measures alone will not be able to prevent irreversible losses, either on land or in the ocean. This is especially the case with rises above 2°C. The restoration of native vegetation, for instance, can improve local resilience to extreme events such as heat waves and flooding, and boost carbon storage, but this is not an alternative to climate action. To protect the Earth and the biodiversity we depend on, we need both to protect ecosystems, giving them a chance to adapt to new conditions, and alleviate further threats from climate change. We can do this by reducing greenhouse gas emissions.


Some of the solutions available for changing our energy and food systems to reduce emissions come with their own biodiversity concerns, however. Bioenergy with carbon capture and storage (BECCS), for example – in which biofuel monocultures are planted for fuel and the carbon produced through burning it is captured, stored and prevented from reaching the atmosphere – is a much-discussed alternative to using fossil fuels. But BECCS will require large areas of land, conflicting with nature protection, as well as potentially interfering in natural ecosystems. Similarly, planting trees for carbon capture is not a silver bullet for climate change – it is instead a tool that requires careful consideration of the risks involved and the proper governance to ensure it is both based on scientific evidence and inclusive of the local communities affected by its use.

What are we doing to solve the biodiversity crisis?

In addition to biodiversity risks being discussed within the scope of climate change, there is a separate track of international work on this challenge. The Convention on Biological Diversity (CBD), which came into force in late 1993, aims to protect biological diversity and to use its components sustainably, in a fair and equitable way. The latest conference of parties to the Convention (CBD COP15), held in Canada at the end of 2022, ended with a landmark pact to halt and reverse nature loss by 2030. This pact included a suite of measures to hold governments to account on their commitments.

Ashden / Ashden

In 2012, to assess and summarise scientific evidence on this issue, governments also established IPBES, an international biodiversity research and policy body. Now counting almost 140 member states, IPBES assesses the state of biodiversity and nature’s contributions to humans in various thematic reports, written and edited by hundreds of volunteer scientists across the world. The two latest reports in the summer of 2022 covered the sustainable use of wild species and the different ways in which people value nature. These IPBES reports concluded that, for example, many of the wild species people depend on for food, energy or income are already in decline, with climate change likely to make this decline even worse. However, it also indicated that addressing these problems through the use of more sustainable practices will go towards alleviating climate impacts.

Useful resources

  • Sir David Attenborough talks about why biodiversity is important in a 5-minute video from the Royal Society.
  • An explainer from Carbon Brief on whether climate change and biodiversity loss can be tackled together.

What does climate change look like?

What does climate change look like?

Rising global temperature is an important sign of ongoing rapid climate change, but there are other signs too.

As the IPCC notes in its latest report on the physical science basis of climate change, it is “unequivocal that human influence has warmed the atmosphere, ocean and land”, while other widespread and rapid changes have occurred as well. With varying degrees of confidence, scientists can link human influence to changes in precipitation, global atmospheric circulation and salinity of near-surface ocean water salinity, plus the global retreat of glaciers since the 1990s, the surface melting of the Greenland ice sheet and the decrease in Arctic sea ice area, especially in summer.

In the ocean, human-caused CO2 emissions have been driving the warming and growing acidification of surface waters, as well as global mean sea-level rise. Human activities may also have contributed to dropping oxygen levels in many upper ocean regions since the mid-20th century. Additionally, as the IPCC notes, changes in the land biosphere since 1970 are consistent with global warming, as climate zones (areas with particular long-term weather patterns) have shifted poleward in both hemispheres. On average, in the Northern Hemisphere each decade since the 1950s has added up to two days to the growing season.

All these changes are being observed and reported by scientists across the world, who then use [attribution science] to look into the links between a particular event and the larger pattern of human influence on the climate. The IPCC analyses this literature to build a comprehensive picture of what climate change looks like beyond a temperature graph alone.

All these large-scale changes in the basic physical parameters of the atmosphere, ocean and land, with added variability across regions, trigger cascades of smaller changes in weather patterns or ecosystems that can create hazards for humans and other living things. Geographic, socioeconomic and other conditions affect how exposed and vulnerable communities are to these hazards and their adverse fallout. This combination of hazards, exposure and vulnerability creates the concept of climate risk, which the IPCC uses in its report on impacts and adaptation as a framework for understanding the “increasingly severe, interconnected and often irreversible impacts of climate change on ecosystems, biodiversity, and human systems.”

While IPCC Working Group I describes the physical science basis of climate change in global average terms, nobody on Earth is actually experiencing these global averages directly: all climate change impacts are local and regional. For this reason, the Working Group II report on impacts and adaptation presents detailed assessments for Africa, Asia, Australasia, Central and South America, Europe and North America, as well as small islands across the globe. It also features several cross-chapter papers on regions that are particularly important for adaptation for a set of unique reasons, such as mountainous and polar regions, deserts, coastal cities or tropical forests and biodiversity hotspots.

The Working Group I report features an interactive tool for looking at the observed and projected climate change information in space and time. The Working Group II report also provides a detailed exploration of the story on climate impacts and adaptation as told in its summary for policymakers. Here, we’ll talk about some of the telltale signs of climate change beyond temperature alone and how they affect people.

How does climate change affect glaciers, permafrost and ice sheets?

The Arctic and Antarctic, as well as vast areas of permafrost and mountain glaciers, constitute the Earth’s cryosphere – our snow and ice environment. These coldest parts of the world are particularly vulnerable to climate change and its impacts, with the cryosphere being a sensitive indicator of these processes. For this reason, the IPCC produced a Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) in 2019.

The most prominent impact of climate change on the cryosphere has been its rapid shrinking: global warming over the last decades has led to ice sheets and glaciers losing their mass, and the Arctic losing its sea ice – this has been getting thinner and ‘younger’ as older, multi-year ice melts away. Moreover, permafrost temperatures have been gradually increasing, with some local thaw damaging infrastructure and exposing people to dangerous diseases such as anthrax. Glacier loss also impacts humans, with many communities in mountainous regions depending on glaciers for their freshwater supply. 

The warming cryosphere can itself impact the climate system, creating so-called feedbacks. Snow and ice have a higher albedo (surface reflectivity) than bare ground, and snow cover insulates soil, preventing it from warming – as snow and ice disappear, and surfaces get darker, they heat up more. Crucially, there is more carbon locked in permafrost than there is currently in the atmosphere – as temperatures rise and the frozen soil thaws, it can become a major source of methane and carbon dioxide.

How does climate change affect coastal areas?

Dhana Kencana / Climate Visuals

Impacts of climate change on coastal areas, ecosystems and human settlements include slow-onset events such as sea-level rise and ocean acidification, as well as an increase in devastating storms and storm surges. According to the IPCC, global mean sea level increased by about 20 centimetres between 1901 and 2018. In some regions, relative (local) sea-level rise can be higher than the global average due to other factors at play, such as tectonic movement or oil exploration.

Coastal habitats are already being lost to erosion of land, permanent inundation and saltwater intrusion, which has consequences for biodiversity, people’s livelihoods, ocean circulation and biogeochemical cycles reaching far beyond the coasts themselves. Additionally, since coastal ecosystems are an important carbon sink – capturing and storing carbon from the atmosphere – their degradation can add to the human-caused pressure on the climate.

As is often the case, climate change worsens the types of existing problems that coastal areas face, such as increasing pressure from urbanisation and economic activity. These climate and non-climate threats can amplify each other and increase the vulnerability of human and natural systems. This is especially relevant given that UN data suggests about 40% of the world’s population lives within 100 kilometres of the coast.

How does climate change affect cities?

Ashden / Ashden

More than half of the world now lives in towns and cities, and the UN expects this number to reach about 5 billion by 2030. This means that cities and their populations bear a lot of current and future climate risks. Impacts such as extreme weather events can cause damage to vital infrastructure, housing and basic services, making residents more vulnerable to these occurrences.

One particular example of the interplay between climate change and urban development has to do with urban heat islands. Big cities – with their sparse vegetation, high population density, and concrete and asphalt in buildings and roads – usually have higher air temperatures than the surrounding areas. This means that heat waves, which are becoming more frequent and intense due to climate change, are much harder to tolerate and survive in an urban environment.

Cities also present many opportunities for solving these problems. UNEP estimates suggest that cities are responsible for 75% of global CO2 emissions, with transport and buildings being among the largest contributors. As such, improving energy efficiency, developing public transportation and addressing other environmental issues in urban areas can both improve well-being and go a long way towards tackling climate change.

To analyse these impacts and opportunities, the IPCC aims to produce a Special Report on climate change and cities in its seventh assessment cycle, which will start in July 2023 and run for five to seven years.

What is the IPCC?


What is the IPCC?

The Intergovernmental Panel on Climate Change (IPCC) provides regular assessments of the scientific basis of climate change, its impacts and future risks, plus options for adaptation and mitigation.

The IPCC was set up in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme. Its purpose is to inform decision-makers and provide the scientific basis for climate policy. This includes the policy negotiations under the UNFCCC (the UN’s Framework Convention on Climate Change). As an intergovernmental organisation, it is open to all member countries of the WMO and United Nations, and currently has 195 members.

Since its inception, the IPCC has prepared six assessment reports – one every six or seven years. It has also delivered a number of special reports on topics such as land, the ocean and cryosphere, extreme events and disasters, and renewable energy. In 2007, the IPCC received the Nobel Peace Prize, jointly with former US Vice President Al Gore, “for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change.”

Member governments task the IPCC with both systematic assessments of research on climate change and specific research questions. For example, in the Paris Agreement signed at the 2015 UN climate conference, parties committed to limit the global average temperature increase to 1.5°C above pre-industrial levels, when human influence on the climate was still negligible – scientists typically use the average temperature for 1850-1900. Following the outcome, countries asked the IPCC to look at what 1.5 degrees of global warming would mean for the Earth and how it would be possible to meet the target. The IPCC agreed and produced a Special Report on Global Warming of 1.5°C, published in 2018.

The IPCC authors report from three groups: Working Group I looks at the physical science basis of climate change, Working Group II explores various impacts of climate change and adaptation, and Working Group III studies ways to reduce our influence on the global climate system. Each group contributes to the assessment report. Additional task forces and groups both help the IPCC keep track of all the data it uses in the reports and assist governments with their greenhouse gas (GHG) inventories.  

For each report, the IPCC recruits hundreds of leading scientists across the world to review the best available research. They then summarise it using the agreed language for various degrees of certainty and the amount of evidence available. For example, for something to be described in the IPCC report as ‘likely’, the probability of this outcome has to be at least 66%. And if something is ‘virtually certain’, like the fact that CO2 emissions from human activity are driving ocean acidification and changes in hot and cold extremes across the world, then its likelihood is higher than 99%.

The draft reports then undergo multiple rounds of extensive review, with thousands of experts providing feedback. Finally, representatives of member governments work with the authors to adopt a comprehensive and accurate summary of each report for policymakers, highlighting the key results of the process,  which are also formally endorsed by IPCC member countries.

What do these reports tell us?

The three parts of the most recent assessment report, AR6, were released in 2021-2022, with a synthesis report following in March 2023. The very first key messages from each of the working group contributions are:

Working Group I: It is unequivocal that human influence has warmed the atmosphere, ocean and land.

Working Group II: Human-induced climate change, including more frequent and intense extreme events, has caused widespread adverse impacts and related losses and damages to nature and people, beyond natural climate variability.

Working Group III: Total net anthropogenic greenhouse gas emissions have continued to rise during the period 2010–2019, as have cumulative net CO2 emissions since 1850. (By ‘net’ the IPCC means emissions from all anthropogenic sources, such as gas-fired power plants, minus the CO2 removed by anthropogenic sinks, such as planted trees.)

As the IPCC itself stresses, while its assessments present projections of future climate change based on different scenarios, the risks climate change poses, and the implications of different response options, they do not tell policymakers what actions to take. This means the assessments are policy relevant, but not policy prescriptive: the IPCC tells governments how they can fight climate change, but does not make recommendations on how they should fight climate change.

For instance, one of the key conclusions of the Special Report on Global Warming of 1.5°C is that, at the current rate of warming, the world will reach the 1.5°C limit some time between 2030 and the early 2050s. The IPCC itself makes no judgement on whether it is smart or necessary to avoid that outcome – instead it is the countries that signed the Paris Agreement that have agreed to the limit. While it can chart all the physically possible pathways to achieve the 1.5°C goal, plus the actions, benefits and costs they would entail, the IPCC gives no preference for any particular pathway – that is for country governments to choose.

Who writes the IPCC reports?

What is the IPCC

Melissa Walsh / IPCC

For each report, the IPCC issues a call to governments and observer organisations to nominate their most qualified scientists studying all aspects of the climate system and our interactions with it. The panel then aims to build a diverse group of authors that both represents a broad range of views and backgrounds, and is equipped to handle the complex task of a comprehensive assessment of the scientific literature.

The aim is to gather people from different regions of the world, balancing representation from developed and developing countries. This helps ensure the resulting text is not biased towards any particular region and does not overlook any locally important questions. The IPCC also encourages younger scientists and those new to the process to get involved in appropriate roles. This is to make sure the writing teams can transfer knowledge and experience, as well as continue to support decision-making with the best available scientific evidence.

Researchers selected by the IPCC become Coordinating Lead Authors, Lead Authors and Review Editors for each assessment report chapter. The IPCC also recruits other experts as Contributing Authors for specific questions within the chapters. All of these scientists volunteer their time and effort, and they follow a specific conflict of interest policy established by the panel.

What sources are used for the reports?

The IPCC does not conduct its own research. In other words, it does not run experiments or gather weather and climate data. Rather, it assesses and synthesises the research published in scientific journals, which has already gone through peer review, and in other reporting sources, such as from governments, industry and research institutions, international and other organisations, and conference proceedings.

All of these sources are carefully evaluated by the chapter teams for quality and validity, and expert reviewers can request copies of anything that is not widely available to further scrutinise the data sources. Review Editors make sure all the comments submitted from both rounds of review are addressed and responded to in writing – for example, any reader can see the more than 51,000 comments and responses in the second draft of the most recent Working Group I report.

Since the IPCC does not do its own research, all information and data used in its reports come with attributions, with full citations for sources listed at the end of each chapter. Additionally, if the authors synthesise several sources for a broader overview, build summary graphics or do similar tasks, they explain their process in captions or footnotes to maintain transparency with both reviewers and readers.

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