► Temperature records were broken across much of the planet, as July-August 2023 were the hottest in the global temperature record, dating back to 1850.

► While some amount of warming is inevitable given the amount of carbon pollution that has already been emitted, neither runaway climate change nor catastrophic impacts are inevitable.

► The upshot of these observations is that warming is accelerating, with increased impacts within and between countries, but humanity has within its power to avoid runaway climate change and to diminish climate impacts through decarbonization, risk reduction, preparedness, and investment in resource management institutions.

This summer has been one of relentless weather-related extreme events, from wildfires in Hawaii, Canada, and the Mediterranean to catastrophic flooding in China and the northeastern United States. While some parts of the world suffered from too much rain, others experienced little or none. Both North and South Korea experienced intense drought in spring 2023, while other parts of the world such as the Horn of Africa and the southwestern United States have experienced multi-year mega-droughts.

Temperature records were broken across much of the planet, as July-August 2023 were the hottest in the global temperature record, dating back to 1850. July was more than a full degree centigrade above the 20th century average. The southwestern U.S. city of Phoenix experienced 31 continuous days of 43 Celsius or more. In coastal Iran, the heat index rose to as high as 70 Celsius, described as “hot tub” like conditions. Even as land temperatures reached historic highs, so too did ocean temperatures. Water temperatures off the coast of Florida reached 38.4 Celsius, creating intolerable conditions for marine life, particularly coral reefs.

A decade or so ago, connecting single extreme weather events to climate change was frowned upon, as at most scientists could say only that these were the kinds of events that we should expect to see with climate change. However, the science of attribution, where scientists are able to say with some precision how much more likely particular events were made by climate change, has matured. To be sure, not all of these events are wholly caused by human-caused climate change. Other natural drivers, such as this year’s El Niño, which have heated ocean temperatures in the eastern and central Pacific, also are affecting global weather patterns.

Nonetheless, we are experiencing dramatic warming, which scientists attribute largely to carbon pollution from human activity. Without faster deployment of the solutions we now have to decarbonize our economy, including renewables and electric vehicles, this warming is expected to accelerate, making events which would have once be rare outliers more and more frequent occurrences.

Those impacts on human lives and well-being are severe, starting with disruptions in food production that have exacerbated food security, particularly in drought-prone poor countries in places like the Horn of Africa, where bad governance and conflict have combined with drought to put millions at risk of famine. Failed rains and failed harvests put pressure on poor farmers to eat their food reserves. When those are gone, they may have to search out emergency rations through camps for internally displaced persons. In regions like the dry corridor of northern Central America, declining economic returns from agriculture have, alongside other drivers, incentivized tens of thousands to look for new opportunities by migrating to the United States.

Understanding and unpacking migration decisions is inherently difficult. Most movements of people are internal within countries, from rural to urban areas. Save for swift onset climate hazards like floods and storms, it is harder to attribute migration decisions to slower onset climate phenomena like droughts.

Nonetheless, we have every expectation that climate change will become a more important driver of migration decisions. A warming world will lead more places on the planet to become too hot to live, with high combined temperatures and humidity occurring regularly. In such places, in the absence of air conditioning, the world will see expanded zones of uninhabitability. People who live or pass through such locations will experience greater risk of heat-related deaths, like the 500 migrant deaths in 2023 as people passed through remote parts of northern Mexico trying to come to the United States.

While some amount of warming is inevitable given the amount of carbon pollution that has already been emitted, neither runaway climate change nor catastrophic impacts are inevitable. First, every tenth of degree of warming that can be avoided will improve the prospects for livability of the planet. While action to reduce levels of carbon dioxide, the main greenhouse gas, will take time because it persists in the atmosphere for more than one hundred years, efforts to reduce gases like methane can appreciably reduce warming in the nearer term because such gases persist in the atmosphere for only about a decade.

Moreover, places that experience climate-related extreme weather events can reduce their risks to harm through early warning and preparedness, even as population grows and climate impacts accelerate. Bangladesh, for example, has experienced catastrophic cyclones that have killed hundreds of thousands of people on more than one occasion. As recently as the early 1990s, Bangladesh experienced a cyclone that killed almost 140,000 people. However, by the 2010s, cyclones of similar magnitude no longer led to mass loss of life. With assistance of international donors, Bangladesh has dramatically improved its capacity and preparedness through investments in improved weather forecasting, early warning systems, and construction of thousands of cyclone shelters. Now, when severe cyclones occur, hardly anyone dies in Bangladesh.

The effects of a worsening climate do not merely stay inside country borders. Countries are linked through transboundary flows of water as well as interlinked markets for goods and services including food. Climate impacts on water and food production can radiate across borders and regions directly or indirectly through markets.

Because water is essential for life, there have been numerous observers who have warned of impending water wars between countries as scarcity affects water supplies. Upstream users are advantaged and can deprive downstream countries from getting access to adequate water supplies, as China has done through dam-building projects on the Mekong and other rivers. Ethiopia’s construction of the Grand Renaissance Dam has inflamed tensions with downstream Egypt, long accustomed to a disproportionate share of water resources along the Nile.

Historically, however, few disputes between countries escalated to armed conflict. Because water is necessary for survival, countries have been able to amicably resolve water disputes, albeit sometimes unequitably. India and Pakistan for example have fought several wars, yet the Indus Water Treaty, signed in 1960, has survived and water was not the central source of contestation in subsequent violent conflicts. Violent water conflicts within countries are more common, with violence in India over the Cauvery River a prominent recent example.

That said, the past is no guarantee that future conflict will be avoided. In a world of intensifying climate change, it may be harder to resolve inter-state and intra-state disputes over water peacefully. With more scarce and irregular rains, countries are tempted to unilaterally dam rivers upstream, without consulting with their neighbors. In many regions, institutions to manage shared waters and resolve disputes are weak or absent, increasing the likelihood conflicts will escalate.

These conflicts aren’t limited to water. Fisheries are another resources which climate change is affecting by changing the habitats of species, with warming waters leading some fish species to migrate to waters more conducive to their survival. This can change the geographic distribution of fish stocks, leading to economic losses from exclusive economic zones and more contestation over international waters and island chain boundaries. There are ample historic instances of militarized disputes over fisheries, and we may see more risk of armed conflict over fish in a world of intensified climate change, without more investment in fisheries management institutions.

The upshot of these observations is that warming is accelerating, with increased impacts within and between countries, but humanity has within its power to avoid runaway climate change and to diminish climate impacts through decarbonization, risk reduction, preparedness, and investment in resource management institutions. Much important work remains to be done.