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.