Climate change: widespread, rapid, and intensifying

According to the latest Intergovernmental Panel on Climate Change (IPCC) Working Group I report, Climate Change 2021: the Physical Science Basis released on August 9, scientists are observing changes in the Earth’s climate in every region and across the whole climate system. Many of the changes observed in the climate are unprecedented in thousands, if not hundreds of 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. Strong and sustained reductions in emissions of carbon dioxide (CO2) and other greenhouse gases would limit climate change.

Hoesung Lee, Chair of the IPCC, remarked that this report reflects extraordinary efforts under exceptional circumstances. The innovations in this report, and advances in climate science that it reflects, have provided an invaluable input into climate negotiations and decision-making.

The report shows that global mean surface temperature has increased by approximately 1℃ since 1850-1900, and finds that global average temperature over the next 20 years is expected to reach or exceed 1.5°C of warming. This assessment is based on improved observational datasets to assess historical warming, as well as progress in scientific understanding of the response of the climate system to human-caused greenhouse gas emissions.

Moreover, the report 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.

IPCC Working Group I Co-Chair Valérie Masson-Delmotte said that this report is a reality check. Now we 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.

IPCC Working Group I Co-Chair Panmao Zhai pointed out that climate change is already affecting every region on Earth in multiple ways. The changes we experience will increase with additional warming.

The report projects that in the coming decades climate change will increase in all regions. For 1.5°C of global warming, there will be increasing 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.

But it is not just about temperature. Climate change is bringing multiple different changes in different regions – which will all increase with further warming. These include changes to wetness and dryness, to winds, snow and ice, coastal areas and oceans.

For the first time, the Sixth Assessment Report provides a more detailed regional assessment of climate change, including a focus on useful information that can inform risk assessment, adaptation, and other decision-making, and a new framework that helps translate physical changes in the climate – heat, cold, rain, drought, snow, wind, coastal flooding and more – into what they mean for society and ecosystems.

The report also shows that human actions still have the potential to determine the future course of climate. The evidence is clear that carbon dioxide (CO2) is the main driver of climate change, even as other greenhouse gases and air pollutants also affect the climate.

Zhai also said that stabilizing 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.

The Working Group I report is the first instalment of the IPCC’s Sixth Assessment Report (AR6), which will be completed in 2022.

Editor: Liu Shuqiao