Editor's Note: This analysis was updated to correct the number of scientific publications referenced.
According to a major report just released by the United Nations Intergovernmental Panel on Climate Change (IPCC), human activities have caused climate change, resulting in a rise in sea levels, reduced crop yields, decreased availability of water for human use, and increased risk of extreme events around the world.
Written by more than 270 leading scientists from 67 countries, the latest report makes clear that the effects of climate change on ecosystems and human well-being are accelerating and worsening, and that our efforts to adapt to risks and withstand hazards must outpace both current and predicted climate change. The report further substantiates scientists’ calls for fast and sustained efforts to reduce emissions across every facet of life as necessary steps to reduce the risks of more damaging effects in the future.
The report, titled “Climate Change 2022: Impacts, Adaptation and Vulnerability,” interweaves social and economic research and data with observed changes to the physical climate—for example, sea-level rise in low-lying coastal communities—to paint an all-encompassing picture of the interconnectedness of Earth’s systems. It stresses how changes to nature and society are likely to proceed in the coming decades as global temperatures rise, and identifies current and future options to better withstand climate impacts as well as their likelihood of success.
The nearly 4,000-page report synthesizes 34,000 scientific publications on the observed and predicted effects of climate change to natural and human systems, as well as the capacity of these systems to withstand change. It outlines how increased warming and sea-level rise affect biodiversity, water availability, agriculture, human settlements, and infrastructure. By doing so, the report builds a strong case that the effects of climate change are being felt everywhere and are predominantly negative.
The report also highlights the intergenerational nature of climate change: Under even the most extreme warming scenarios, people over age 55 are unlikely to live to see its worst outcomes. In reviewing the available evidence, the report identifies key risks at global and regional scales and proposes climate resilient development pathways across sectors and geographies.
Average global temperatures have risen more than 1 degree Celsius (2 degrees Fahrenheit) since the end of the 19th century. This warming has already impacted ecosystems and societies, and increased changes are certain to occur because of ongoing emissions.
Central to the report is evidence that rising temperatures could push our planet beyond tipping points at which changes can no longer be avoided or undone. All species, including humans, have certain adaptation limits, above which preventing or withstanding the effects of climate change is not possible. Species, such as the rodent Bramble Cay melomys in Australia, have suffered climate-induced extinctions, while others have shifted their habitats in response to temperature rise. If warming reaches 1.5 C (2.7 F), as many as 14% of terrestrial species could face a high risk of extinction, up to 24% of the world’s population would be exposed to flooding, and fully 90% of coral reefs could disappear. At 2 C (3.6 F) of warming, these numbers could rise to 18%, 30%, and 99%, respectively.
This science makes clear that incremental temperature increases result in increased effects—regardless of the amount of warming that has already occurred. About 3.3 billion people currently live in areas of high vulnerability to climate change. Managing emissions to limit future warming to a maximum of 1.5 C (2.7 F) substantially reduces future losses and damages when compared with higher levels of warming. In other words, the magnitude of change to natural and human systems—including the likelihood of severe and irreversible impacts, losses, and damages —increases with the magnitude of future warming.
Ultimately, while some of these consequences are already being observed—such as increased droughts, more intense flash flooding, and elevated storm surges—the worst effects can still be avoided through better planning and adapting to changing climatic conditions. However, even if future warming is limited to 1.5 C (2.7 F), some impacts will be irreversible as ecosystem-specific limits to adaptation may be exceeded. For example, some coral reefs, polar regions, and ecosystems found on the slopes of mountains have already reached or surpassed limits to adaptation.
The IPCC report underlines the interconnectedness of all systems on Earth, including climate, biodiversity, ecosystems, and human societies. What’s become unequivocally clear is that effects to one translate to effects for all. And that reducing the magnitude of future climate change benefits ecosystems and reduces the risk to society.
Although a range of useful options exists to adapt to climate change across regions and sectors—from protecting coastal wetlands that buffer shorelines from sea-level rise to promoting the interconnectivity of protected areas to allow for shifting migration and developing flood-prepared communities—they lose their effectiveness at higher levels of warming. As such, efforts to reduce vulnerability to climate risks and increase capacity to withstand effects from future changes must be implemented while also ensuring that global emissions are rapidly curtailed to limit future warming.
The report highlights that climate change will result in transformational change on a global scale. The question is what this change will look like as the “window of opportunity to secure a livable and sustainable future for all” is rapidly closing. We can choose to live in a hotter and deadlier future for people and nature. Or, by rapidly reducing emissions, redesigning energy systems, and aggressively adapting to climatic impacts, we can choose to avoid the worst effects of climate change.
Courtney Durham is an officer focusing on The Pew Charitable Trusts’ international conservation work, and Jim Palardy is a project director with Pew’s conservation science project.