The Working Group I contribution to the Sixth Assessment Report, Climate Change 2021: The Physical Science Basis is now out.
According to the latest report from the Intergovernmental Panel on Climate Change (IPCC), published on August 9, 2021, scientists are observing changes in the Earth’s climate in all regions and in the climate system as a whole. Many of the observed changes in climate are unprecedented in thousands, but hundreds of thousands of years, and some of the changes that are already taking place, such as continued sea level rise, will not be reversible for several weeks. centuries or millennia. However, a substantial and sustained reduction in carbon dioxide (CO2) and other greenhouse gas emissions would limit climate change. Although improvements in air quality would be rapid, it could take 20 to 30 years for global temperatures to stabilize, according to the IPCC Working Group I report.
The report offers new estimates of the probability of exceeding the global warming level of 1.5 ° C in the coming decades, and concludes that unless greenhouse gas emissions are reduced immediately, rapidly now. On a large scale, limiting warming to around 1.5 ° C or even 2 ° C will be an unattainable goal. According to this report, greenhouse gas emissions from human activities are responsible for a warming of approximately 1.1 ° C from 1850-1900, and the global average temperature over the next 20 years is projected to reach or exceed a 1.5 ºC heating. This data is the result of the improvement of observational data sets to evaluate historical warming, as well as progress in scientific knowledge of the response of the climate system to greenhouse gas emissions produced by humans. “This report is a reality check,” said IPCC Working Group I Co-Chair Valérie Masson-Delmotte. “We now have a much clearer vision of the past, present and future climate, which is essential to understand where we are going, what can be done and how we can prepare.“
“Climate change already affects all regions of the Earth in multiple ways. Any increase in warming will exacerbate the changes we are experiencing, ”said IPCC Working Group I Co-Chair Panmao Zhai. The report’s projections indicate that climate change will increase in all regions in the coming decades. According to the report, with global warming of 1.5 ° C, there will be an increase in heat waves, warm seasons will lengthen and cold seasons will shorten; while with a global warming of 2 ° C, extreme heat events would more frequently reach critical tolerance thresholds for agriculture and health. However, it is not just a matter of temperature. As a consequence of climate change, different regions experience different changes, which will intensify if warming increases; in particular, changes in humidity and dryness, winds, snow and ice, coastal areas and oceans. For example:
– Climate change is intensifying the hydrological cycle. This leads to increased rainfall and associated flooding, as well as more intense droughts in many regions.
– Climate change is affecting precipitation patterns. At high latitudes, precipitation is likely to increase, while it is expected to decrease in much of the subtropical regions. Changes in monsoon rainfall are expected, which will vary by region.
– Coastal areas will experience continuous sea level rise throughout the 21st century, contributing to coastal erosion and more frequent and severe coastal flooding in low-lying areas. Extreme sea level events that formerly occurred once every 100 years could be recorded annually by the end of this century.
– Further warming will amplify the melting of permafrost, as well as the loss of seasonal snow cover, the melting of glaciers and ice sheets, and the loss of Arctic sea ice in summer.
– Changes in the ocean, such as ocean warming and acidification, increased frequency of marine heat waves, and reduced oxygen levels, are clearly related to human influence. These changes affect both ocean ecosystems and the people who depend on them, and will continue to occur for at least the rest of the century.
– In the case of cities, some aspects of climate change can be amplified, in particular heat (as urban areas are often warmer than their surroundings) and floods due to episodes of heavy rainfall and rising sea levels in coastal cities.
The Sixth Assessment Report provides for the first time a more detailed analysis of climate change at the regional level – paying particular attention to useful information that can serve as the basis for risk assessment, adaptation and other decision-making – as well as a new framework that helps translate physical climate changes – 3 – (heat, cold, rain, drought, snow, wind, coastal flooding, etc.) into what they represent for society and ecosystems.