Escalating Environmental, Economic, and Societal Risks

Unabated heat stress is already causing changes, with damaging effects on communities, infrastructure, and the natural systems that sustain life. Even with success in reaching targeted emissions reduction under the Paris Agreement, warming is predicted to reach 2.5 to 3 °C by the end of this century, with a high risk of devastating effects on natural systems and human populations in the next 10 to 30 years. Uncertainties in the responses of natural systems to unprecedentedly fast-changing conditions means that current model projections could also underestimate the pace and severity of changes.

Tipping Points and Cascading Changes

As heat stress builds on natural systems, they can reach points of rapid change or collapse — “tipping points.” This poses major risks to safety, in both the rapid escalation of direct impacts, such as rapid sea level rise resulting from the collapse of a major ice sheet, and in accelerating changes in other natural systems — “cascade effects,” such as warming caused by massive release of greenhouse gases from melting permafrost. Leading experts warn of significant risk of crossing major tipping point thresholds in the next 10 to 30 years, including some we may have crossed already.

Exposure to Near-Term Risk

The current portfolio of responses to climate change centers on reducing CO2 in the atmosphere by reducing emissions or actively removing it. This is critical to the health of the climate system, but acts on heat energy in the system relatively slowly. Even with aggressive emissions reduction and use of carbon removal techniques, society is many decades away from the warming that is stressing natural and human systems, leaving us exposed to uncertain, catastrophic risks in the near term. We face a critical gap in responses that could substantially reduce warming within a decade or two, leaving these high near-term risks unaddressed.

The impact of warming climate on human health is profound. A recent study found that at 1.5 °C of warming, 16% of the world’s population in 2050 (i.e., 1.5 billion people) will have high levels of risk in at least one of three main sectors — water, energy and food, and environment. At 2 °C, this almost doubles to 29% of the global population (i.e., 2.7 billion people). By 2070, the environment for 1/3 of the world’s people may no longer be livable. In many regions, extreme heat is also likely to increase the risk of infectious diseases and related deaths. Severe heat also has detrimental impacts on workers, increasing the rate of accidents, heat exhaustion, and heat stroke such that by 2030, extreme heat could lead to trillions in lost labor productivity.

Increased heat and related impacts is likely to lead to increased political instability, large-scale migration, intensifying competition for resources (water, food, etc.), and other security risks. Recent analyses project that warming climate could displace between 143 million and 1.5 billion people by 2050, with greater effects on developing nations and vulnerable populations less responsible for the causes of warming. With more areas uninhabitable, higher instances of drought, crop failure, flooding, storms, and mass migration are projected, with effects on social and political stability and increased risk of armed conflict, creating unprecedented humanitarian and security challenges for all nations.

The effects of climate change on infrastructure and economic systems are profound. Buildings, bridges, dams, underground infrastructure, and other structures are at risk as land and surface conditions move beyond the range of stresses that they are engineered to withstand. Flooding and storm surges threaten major facilities like coastal nuclear reactors, military installations, city centers, and sewage systems. Transportation disruption will grow increasingly severe, with flights disrupted by heat and storms, shipping impaired by storms, and ground transportation impacted by storms and flooding. The cost of the combined impacts of climate change on the global economy is forecast to be trillions of dollars by 2050.

There are numerous risks to land-based systems as warming rises, including increased severity and intensity of drought, wildfires, and extreme heat and precipitation, leading to habitat losses and the extinction of keystone species. The cumulative impacts of variable weather, changing conditions, diseases, pests, drought, flood, and soil erosion are already damaging some sectors and may cause a sharp drop in agricultural output, as global yields of wheat, barley, and corn decrease with increasing global average temperature. Record temperatures in cold regions are also melting frozen soil (permafrost) that contains massive quantities of greenhouses gases, release of which could rapidly and dramatically accelerate warming.

More than 90 percent of the heat energy from human emissions between 1971 and 2010 has been absorbed by the ocean. This additional heat is impacting ocean ecosystems — from coral collapse, to mangrove loss, to increased harmful algae blooms. In the next 20 years, studies forecast a loss of nearly all of the world’s coral — the habitats that support 25 percent of all ocean life — and dramatic losses of saltwater fish. Ocean life, particularly the small organisms at the surface (e.g., phytoplankton), is also a critical source of the atmosphere’s oxygen Their populations have already declined as much as 40 percent since 1950 due to rising sea temperatures. Warming is also causing sea levels to rise and circulation to change, increasing weather extremes around the world.

Sea ice covers about 11 percent of the world’s oceans depending on the season. The amount of ice regulates the climate and affects the reflection of sunlight (albedo), salinity, and ocean-atmosphere thermal exchange. The Earth’s polar regions are warming 2-3 times as fast as the rest of the world, with the highest ever recorded temperatures in the Arctic in 2020. Warm Arctic summers have been linked with extreme weather and a decrease in the proportion of sunlight that is naturally reflected from the Earth’s surface, accelerating warming. As polar regions warm, the stability of major ice sheets is threatened, increasing the possibility for rapid, extreme sea-level rise and substantial changes in ocean and atmospheric circulation.