Editor's Note: This was updated on August 16, 2021 to highlight the science of the report findings.
Longer heat waves, more intense rainfall, rising sea levels, and melting ice caps are some of the effects of climate change that are happening now and almost certain to worsen in coming years, according to the latest report from the United Nations Intergovernmental Panel on Climate Change (IPCC).
The report, Climate Change 2021: The Physical Science Basis, offers a sobering account of how human activities have altered Earth’s climate and what those changes might mean for people around the world. It carries an urgent warning that we must act quickly to prevent the worst-case scenarios from playing out. The report also includes a first-of-its-kind regional assessment of climate change, offering an interactive guide to inform risk assessment, adaptation, and other decision-making.
Nearly 4,000 pages long, the report finds unequivocal evidence that human activities have warmed the atmosphere, ocean, and land. The widespread and rapid changes are already driving weather and climate extremes in every region of the planet, from wildfires and droughts to massive flood, tropical cyclones, and more.
The report cites a growing compendium of evidence that the global surface temperature—on land and sea—is rising, and that the rise is accelerating.
“Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2,000 years,” the IPCC wrote, adding that “[E]ach of the last four decades has been successively warmer than any decade that preceded it since 1850.”
And although the report details strategies to stabilize the climate, some of the effects that are already upon us are irreversible, especially changes in the ocean, ice sheets, and sea level. The Southern Ocean around Antarctica, for example, is experiencing the strongest ocean heat uptake in the world, penetrating to the deep layers and affecting the chemistry and temperature of these waters. Critically, this could disrupt the Antarctic ocean currents, which pull nutrients from deep in the Southern Ocean and ferry them to major ocean basins across the planet.
The assessment finds that global warming of 1.5°C (2.7 F) and 2°C (3.6 F) above pre-industrial levels will probably be exceeded in the next 20 to 30 years and details the need for rapid emissions reductions and other action to adapt to and build resilience against climate impacts. Nature conservation is one of several strategies identified in the report for addressing climate change. For example, conserving and restoring coastal wetlands and seagrass meadows can help mitigate climate change because those ecosystems can sequester and store significant amounts of CO2, often referred to as blue carbon. Protecting coastal ecosystems can also help stabilize shorelines and buffer communities from storms and floods. Conversely, disturbing these and other natural areas such as forests and peatlands can release massive volumes of CO2 into the atmosphere, further speeding up climate change. Although nature-based solutions such as these can not solve the climate crisis alone, they can be part of the solution while preserving biodiversity and providing continued socioeconomic values for communities.
The report emphasizes that rapid, strong, and sustained action to reduce emissions of carbon dioxide and other greenhouse gases and air pollutants, especially methane, can improve the future course of the climate. The assessment solidifies a robust knowledge base that our climate is changing and that leaders and practitioners need to respond with urgency and awareness at all levels, including the upcoming 26th Conference of the Parties at the United Nations Framework Convention on Climate Change and the 15th Conference of the Parties for the Convention on Biodiversity.
The analysis was completed by 234 authors from 66 countries, includes over 14,000 cited references, and reflects more than 75,000 comments from experts and government representatives. It is the first of four reports slated over the next year that build on previous IPCC papers, including the 2018 Special Report: Global Warming of 1.5oC. The four reports will comprise the IPCC’s Sixth Assessment and are intended to assess and communicate the latest science on our changing climate. Decision-makers around the world needn’t wait for the next installment in order to act. Indeed, as the newest warning makes clear, any further stalling at this point might be construed as surrendering to a grim future.
Courtney Durham is an officer with Pew’s international conservation unit, and Jim Palardy is a project director with Pew’s conservation science program.