If the world fails to reverse climate change, the consequences will compound across nearly every system humans depend on: food, water, health, economies, and the natural world. These aren’t distant hypotheticals. Many are already underway, and the difference between acting now and not acting is measured in millions of lives, trillions of dollars, and potentially irreversible damage to Earth’s climate system. Here’s what the evidence projects.
Food Production Would Decline as Demand Rises
Global agriculture is already feeling the strain. Between 1961 and 2014, droughts alone reduced maize yields by 3 to 10% and soybean yields by 3 to 12% in the world’s top-producing countries. Those numbers are projected to worsen significantly through 2050 as droughts become more frequent and severe.
The problem isn’t just that individual harvests shrink. Population growth means the world will need roughly 50% more food by mid-century. Staple crops like wheat, rice, maize, and soybeans face compounding threats: hotter growing seasons, shifting rainfall patterns, and longer droughts. Regions near the equator, which are already warm, would be hit hardest. Countries in sub-Saharan Africa and South Asia, where hundreds of millions of people already face food insecurity, have the least capacity to adapt. The result is a widening gap between how much food the world needs and how much it can grow.
Heat Would Kill Far More People
Heat-related deaths are projected to rise dramatically. One study of 44 U.S. cities estimated that heat-related summer mortality could increase by 70 to over 100% by 2050, compared to historical baselines, even accounting for some degree of human acclimatization. Winter mortality would drop slightly as cold snaps become less severe, but nowhere near enough to offset the summer increase.
Older adults face the greatest risk. Projections for Washington State found that people over 65 could see excess heat deaths roughly triple between 2025 and 2085. In cities across South Asia, the Middle East, and parts of Africa, where temperatures already push the limits of human tolerance, the threat is even more acute. Prolonged heat waves don’t just cause heatstroke. They worsen heart disease, kidney failure, and respiratory illness. They also make outdoor work dangerous, which hits agricultural and construction workers hardest.
Economies Would Shrink, Unevenly
The economic damage scales steeply with temperature. A 2025 Congressional Budget Office analysis found that at 2°C of warming above pre-industrial levels, GDP losses average around 0.9%. At 3°C, that jumps to 4.4%. At 4°C, losses reach 6.9%. Those percentages may sound modest, but applied to the scale of the U.S. economy alone, they represent trillions of dollars in lost output every year.
The costs come from everywhere: damaged infrastructure, lower agricultural productivity, healthcare spending, disaster recovery, lost labor productivity from heat, and disrupted supply chains. Poorer nations, which have contributed the least to emissions, face the steepest losses because their economies depend more on agriculture and outdoor labor, and they have fewer resources to rebuild after disasters. This is one of the core injustices of unchecked warming: the countries least responsible bear the greatest burden.
Seas Would Rise One to Five Feet
Under a high-emissions scenario, global sea levels are projected to rise between roughly 0.5 and 1.7 meters (about 1.5 to 5.4 feet) by 2100. The wide range reflects uncertainty about how fast ice sheets in Greenland and Antarctica will break apart. Even the low end of that range would be devastating for coastal cities.
A one-meter rise would put major portions of Miami, Jakarta, Shanghai, Mumbai, and dozens of other coastal cities at risk of regular flooding. Low-lying island nations like Tuvalu and the Maldives could become largely uninhabitable. Saltwater intrusion into freshwater aquifers would threaten drinking water for millions of people who live nowhere near the coast. And these aren’t one-time floods. Rising seas mean permanent loss of land, higher storm surges, and increasingly expensive infrastructure just to hold back the water.
Hundreds of Millions Could Be Displaced
The World Bank’s Groundswell report projects that without meaningful climate and development action, as many as 216 million people could be forced to move within their own countries by 2050. These are internal migrants, people displaced by drought, crop failure, rising seas, and water scarcity who relocate to other parts of their home country. The figure doesn’t include people who cross international borders.
The six regions studied (Latin America, Sub-Saharan Africa, South Asia, East Asia and the Pacific, North Africa, and Eastern Europe and Central Asia) would all see significant movement from rural areas to cities. This creates cascading problems: overwhelmed urban infrastructure, competition for jobs and housing, and political instability. Climate migration is already happening in parts of Central America, the Sahel, and Bangladesh. Without intervention, it accelerates into one of the defining humanitarian crises of the century.
Species Loss Could Be Massive
Estimates of how many species the planet could lose to climate change vary widely, from roughly 1% to as high as 70% depending on the study and the warming scenario. But worst-case estimates from large-scale analyses tend to converge around 20 to 30% of species lost. More recent preliminary forecasts suggest 14 to 32% of macroscopic species (those visible to the naked eye) could face climate-driven extinction within the next 50 years.
Coral reefs are among the most vulnerable ecosystems. At 2°C of warming, virtually all tropical coral reefs are expected to suffer severe bleaching, and most would not recover. Arctic and alpine species have nowhere cooler to migrate to. Pollinators, which underpin roughly a third of global food production, face habitat loss and timing mismatches with the plants they depend on. Biodiversity loss isn’t just an environmental tragedy. It weakens ecosystems that provide clean water, soil fertility, pest control, and flood protection for human communities.
Tipping Points Could Make Warming Irreversible
Perhaps the most alarming dimension of inaction is the risk of crossing climate tipping points, thresholds beyond which certain changes become self-reinforcing and essentially permanent on human timescales.
Greenland is already losing 30 million tons of ice every hour. Current assessments suggest its melting could become unstoppable at around 1.5°C of warming, a threshold the world is on track to cross within the next decade. Arctic permafrost, which stores vast amounts of frozen methane (a greenhouse gas far more potent than carbon dioxide over short timescales), is already thawing. As it releases that methane, it accelerates warming, which thaws more permafrost, creating a feedback loop humans cannot control.
The Atlantic Meridional Overturning Circulation, the ocean current system that includes the Gulf Stream and keeps northwestern Europe relatively mild, is another major concern. Some researchers have argued it could shut down within the next 20 to 30 years without aggressive emissions reductions. If it collapses, northwestern Europe would face prolonged severe winters, while rainfall patterns across the tropics would shift dramatically, disrupting monsoons that billions of people depend on for agriculture.
A 2025 analysis found that if the world fails to return to 1.5°C of warming by the end of the century, there is roughly a one in four chance that at least one major global tipping point will be crossed: the collapse of the Atlantic current system, the Amazon rainforest ecosystem, or the Greenland or West Antarctic ice sheet. Once any of these tips, the consequences play out over decades to centuries, regardless of what emissions policies are adopted afterward. That is the core danger of delay. Some of these changes, once set in motion, cannot be taken back.