This August 9th, 2021, the Intergovernmental Panel on Climate Change (IPCC) publishes “Climate Change 2021: The Physical Science Basis” report (Working Group 1 report),: first part of a series of 3 reports that will end with the publication of the Synthesis Report in September 2022.
Resulting from the work of 234 authors from 66 different countries, this assessment builds on 14.000 peer-reviewed articles and 78.000 reviewing comments to which the OCP contributed. It is the most important knowledge assessment on climate change since 2013. Thanks to major scientific advances, this report sheds new light on past, present and future paths of climate change and modelises its projections around 5 scenarios of greenhouse gases emissions (GHG). “We have now a clearer picture of past, present and future climate, which is essential to understand where we are heading towards, what can be done and how we can prepare” declared Valérie Masson Delmotte, co-chair of IPCC’s Working Group I, who speaks of this report as a “reality check”.
The message carried out by the IPCC is straightforward: recent climate changes are widespread, and unprecedented for thousands of years. It is still possible to keep global warming under 1.5°C, but to do so, the reduction of global emissions has to be rapid and drastic.
Human activities: main drivers of climate change
The report makes it very clear that human activities are responsible for climate change. Through a comparison of greenhouse gas emissions from human activities with those from natural cycles and internal variability, the IPCC report shows that about 1.1 ° C of the rise in temperatures since 1850-1900 can be attributed to human activities.
Climate change is widespread, rapid and unprecedented
Many of the changes observed in the climate are unprecedented in thousands of years. Scientific evidence showed that the last four decades have been the warmest ever recorded since 1850-1900 and that carbon dioxide concentration rates have been the highest in 2 million years. These patterns could continue to rise and accelerate without a rapid, drastic and sustained reduction of greenhouse gases emissions, in particular with dropping capacity of carbon absorption by marine and land “carbon sinks” due to the higher carbon concentration in the atmosphere. Thus, temperatures are predicted to increase under all IPCC scenarios. This rise could exceed the 1.5°C target and reach 3°C as early as 2050 in the absence of a rapid drop of carbon dioxide in the next decade.
The impacts of climate change are already visible in every part of the world
Climate change is a global phenomenon whose impacts are already felt throughout the entire world. WGI report shows that beyond global warming, other phenomena are becoming more intense and frequent and are going to affect natural and human systems. The impacts of climate change are already visible on the water cycle with more intense rainfall associated with floods in some areas and droughts in others; the rising sea level along with significant risk of submersion; the intensification of extreme events; the melting of glaciers and permafrost with a 40% retreat of the Arctic Ocean since 1979; the increase in temperatures and frequency of heat waves in the ocean as well as its acidification and deoxygenation.
These changes are global but their effects are felt differently regionally. In this respect, the IPCC proposes a regional analysis seeking to inform risk assessment and management as well as adaptation decision-making. This report includes a new impact-driven framework which aims to translate physical changes of the climate (heat, cold, rain, drought, snow, wind, coastal flood etc.) into impacts for human societies and the ecosystems. In addition, an Interactive Atlas and regional factsheets will allow to highlight local observations of current and foreseeable evolutions.
Urgent need for a strong, rapid and sustained reduction of global greenhouse gases emissions
Rising sea levels, increasing temperatures at depth, decreasing ice sheets are all profound and long-term changes that are expected to continue on the scale of a human lifetime. Yet, the magnitude of these global changes depends fundamentally on the trajectory of greenhouse gas emissions. As pointed out in the report, rising temperatures and their consequences are a function of growing CO2 emissions. In other words, each additional emission of carbon dioxide contributes to worsening global changes. The report therefore insists on the need to achieve net zero emissions in order to limit the rise in temperatures to 2°C by 2050.
Published three months ahead of UNFCCC COP26, this report sounds the alarm bell on the urgent need to act. While only 110 states have already submitted their Nationally Determined Contribution (new or updated), this report marks a crucial step in the stepping up of global ambitions to reach Paris Agreement’s targets, and shall be an essential tool for international climate negotiations. In this regard, the IPCC recalled that while all political stakeholders, companies, investors and citizens have to play their part, the G20 States, as emitters of 80% of global GHG emissions, have the responsibility to set ambitious goals and the power to drastically reduce their emissions.
Anaïs Deprez, Sarah Palazot