Scientists are observing changes in the earth’s climate in every region and across the whole climate system, according to the latest Intergovernmental Panel on Climate Change (IPCC) report.
Many of the changes observed in the climate are unprecedented in thousands of years, and some of the changes already set in motion — such as continued sea level rise — are irreversible over hundreds to thousands of years, the report says.
However, strong and sustained reductions in emissions of carbon dioxide (CO2) and other greenhouse gases would limit climate change, the IPCC says. While benefits for air quality would come quickly, it could take 20-30 years to see global temperatures stabilise, according to the IPCC Working Group I report, Climate Change 2021: the Physical Science Basis, approved by 195 national governments within the United Nations.
The Working Group I report is the first instalment of the IPCC’s Sixth Assessment Report (AR6), which will be completed in 2022.
The report provides new estimates of the chances of crossing the global warming level of 1.5°C in the next decades, and finds that unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5°C or even 2°C will be beyond reach.
Analysis specific to the UK and Scandinavia includes an observed increase in pluvial flooding attributed to human influence and projected to further increase at global warming of 1.5°C (medium confidence) and 2°C and above. On the other hand, river flooding is projected to decrease at global warming of 2°C and above.
The report shows that emissions of greenhouse gases from human activities are responsible for approximately 1.1°C of warming since 1850-1900, and finds that averaged over the next 20 years, global temperature is expected to reach or exceed 1.5°C of warming, bringing more heat waves, longer warm seasons and shorter cold seasons. At 2°C of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and health, the report shows.
This assessment is based on improved observational datasets to assess historical warming, as well progress in scientific understanding of the response of the climate system to human-caused greenhouse gas emissions.
“This report is a reality check,” said IPCC Working Group I co-chair Valérie Masson-Delmotte. “We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare.”
Climate change is affecting rainfall patterns. In high latitudes, precipitation is likely to increase, while it is projected to decrease over large parts of the subtropics. Changes to monsoon precipitation are expected, which will vary by region. Coastal areas will see continued sea level rise throughout the 21st century, contributing to more frequent and severe coastal flooding in low-lying areas and coastal erosion. Extreme sea level events that previously occurred once in 100 years could happen every year by the end of this century.
Further warming will amplify permafrost thawing, and the loss of seasonal snow cover, melting of glaciers and ice sheets, and loss of summer Arctic sea ice.
“Changes to the ocean, including warming, more frequent marine heatwaves, ocean acidification, and reduced oxygen levels have been clearly linked to human influence,” the report asserts. “These changes affect both ocean ecosystems and the people that rely on them, and they will continue throughout at least the rest of this century. For cities, some aspects of climate change may be amplified, including heat (since urban areas are usually warmer than their surroundings), flooding from heavy precipitation events and sea level rise in coastal cities.”
The report also says that human actions still have the potential to determine the future course of climate.
“Stabilising the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions, and reaching net zero CO2 emissions. Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate,” said the other co-chair, Panmao Zhai.
British ecologist Robert Spencer, a director with construction consultant Aecom, said: “The latest IPCC report sends the clearest message yet on the need for urgent action if we are to avert the worst impacts of climate change. COP26 will help clarify where investments and activities should be prioritised, transforming promises into funded and much-needed, widespread action.
“Some aspects of climate change are now inevitable, and we need to be ready to respond to expected threats. For the built environment sector, driving in resilience to anticipate, absorb and recover from the effects of climate related events should be at the forefront of everything we do now.
“As an industry, the greatest impact will be felt through our collaborative action. We must use our collective expertise, working with clients and supply chains, to play our crucial part in tackling the climate and biodiversity emergencies. As a knowledge-based sector, we will need to use our skills and capabilities to raise awareness and provide training and solutions that will rapidly support our clients and communities on their journeys to net zero.”