Effects of climate change
Effects of climate change are well documented and growing for Earth's natural environment and human societies. Changes to the climate system include an overall warming trend, changes to precipitation patterns, and more extreme weather. As the climate changes it impacts the natural environment with effects such as more intense forest fires, thawing permafrost, and desertification. These changes impact ecosystems and societies, and can become irreversible once tipping points are crossed. Climate activists are engaged in a range of activities around the world that seek to ameliorate these issues or prevent them from happening.
The effects of climate change vary in timing and location. Up until now the Arctic has warmed faster than most other regions due to climate change feedbacks. Surface air temperatures over land have also increased at about twice the rate they do over the ocean, causing intense heat waves. These temperatures would stabilize if greenhouse gas emissions were brought under control. Ice sheets and oceans absorb the vast majority of excess heat in the atmosphere, delaying effects there but causing them to accelerate and then continue after surface temperatures stabilize. Sea level rise is a particular long term concern as a result. The effects of ocean warming also include marine heatwaves, ocean stratification, deoxygenation, and changes to ocean currents. The ocean is also acidifying as it absorbs carbon dioxide from the atmosphere.
The ecosystems most immediately threatened by climate change are in the mountains, coral reefs, and the Arctic. Excess heat is causing environmental changes in those locations that exceed the ability of animals to adapt. Species are escaping heat by migrating towards the poles and to higher ground when they can. Sea level rise threatens coastal wetlands with flooding. Decreases in soil moisture in certain locations can cause desertification and damage ecosystems like the Amazon rainforest. At of warming, around 10% of species on land would become critically endangered.
Humans are vulnerable to climate change in many ways. Sources of food and fresh water can be threatened by environmental changes. Human health can be impacted by weather extremes or by ripple effects like the spread of infectious diseases. Economic impacts include changes to agriculture, fisheries, and forestry. Higher temperatures will increasingly prevent outdoor labor in tropical latitudes due to heat stress. Island nations and coastal cities may be inundated by rising sea levels. Some groups of people may be particularly at risk from climate change, such as the poor, children, and indigenous peoples. Industrialised countries, which have emitted the vast majority of CO2, have more resources to adapt to global warming than developing nations do. Cumulative effects and extreme weather events can lead to displacement and migration.
Changes in temperature
Global warming affects all parts of Earth's climate system. Global surface temperatures have risen by. Scientists say they will rise further in the future. The changes in climate are not uniform across the Earth. In particular, most land areas have warmed faster than most ocean areas. The Arctic is warming faster than most other regions. Night-time temperatures have increased faster than daytime temperatures. The impact on nature and people depends on how much more the Earth warms.Scientists use several methods to predict the effects of human-caused climate change. One is to investigate past natural changes in climate. To assess changes in Earth's past climate scientists have studied tree rings, ice cores, corals, and ocean and lake sediments. These show that recent temperatures have surpassed anything in the last 2,000 years. By the end of the 21st century, temperatures may increase to a level last seen in the mid-Pliocene. This was around 3 million years ago. At that time, mean global temperatures were about warmer than pre-industrial temperatures. The global mean sea level was up to higher than it is today. The modern observed rise in temperature and concentrations has been rapid. Even abrupt geophysical events in Earth's history do not approach current rates.
How much the world warms depends on human greenhouse gas emissions and on how sensitive the climate is to greenhouse gases. The more carbon dioxide is emitted in the 21st century the hotter the world will be by 2100. For a doubling of greenhouse gas concentrations, the global mean temperature would rise by about. If emissions of stopped abruptly and there was no use of negative emission technologies, the Earth's climate would not start moving back to its pre-industrial state. Temperatures would stay at the same high level for several centuries. After about a thousand years, 20% to 30% of human-emitted would remain in the atmosphere. The ocean and land would not have taken them. This would commit the climate to a warmer state long after emissions have stopped.
With current mitigation policies the temperature will be about 2.7 °C above pre-industrial levels by 2100. It would rise by if governments achieved all their unconditional pledges and targets. If all the countries that have set or are considering net-zero targets achieve them, the temperature will rise by around. There is a big gap between national plans and commitments and the actions that governments have taken around the world.
Weather
The lower and middle atmosphere, where nearly all weather occurs, are heating due to the greenhouse effect. Evaporation and atmospheric moisture content increase as temperatures rise. Water vapour is a greenhouse gas, so this process is a self-reinforcing feedback.The excess water vapour also gets caught up in storms. This makes them more intense, larger, and potentially longer-lasting. This in turn causes rain and snow events to become stronger and leads to increased risk of flooding. Extra drying worsens natural dry spells and droughts. This increases risk of heat waves and wildfires. Scientists have identified human activities as the cause of recent climate trends. They are now able to estimate the impact of climate change on extreme weather events using a process called extreme event attribution. For instance such research can look at historical data for a region and conclude that a specific heat wave was more intense due to climate change. In addition, the time shifts of the season onsets, changes in the length of the season durations have been reported in many regions of the world. As a result of changes in climatic patterns and rising global temperatures, extreme weather events like heatwaves and heavy precipitation are occurring more frequently and with increasing severity.
Heat waves and temperature extremes
Heatwaves over land have become more frequent and more intense in almost all world regions since the 1950s, due to climate change. Heat waves are more likely to occur simultaneously with droughts. Marine heatwaves are twice as likely as they were in 1980. Climate change will lead to more very hot days and fewer very cold days. There are fewer cold waves.
Experts can often attribute the intensity of individual heat waves to global warming. Some extreme events would have been nearly impossible without human influence on the climate system. A heatwave that would occur once every ten years before global warming started now occurs 2.8 times as often. Under further warming, heatwaves are set to become more frequent. An event that would occur every ten years would occur every other year if global warming reaches.
Heat stress is related to temperature. It also increases if humidity is higher. The wet-bulb temperature measures both temperature and humidity. Humans cannot adapt to a wet-bulb temperature above. This heat stress can kill people. If global warming is kept below, it will probably be possible to avoid this deadly heat and humidity in most of the tropics. But there may still be negative health impacts.
There is some evidence climate change is leading to a weakening of the polar vortex. This would make the jet stream more wavy. This would lead to outbursts of very cold winter weather across parts of Eurasia and North America and incursions of very warm air into the Arctic. Some studies found a weakening of the AMOC by about 15% since 1950, causing cooling in the North Atlantic and warming in the Gulf Stream region. Climate change is expected to weaken AMOC in all emissions scenarios and, in some high emissions scenarios, can bring it to collapse. This can result in cooling of some parts of Europe by up to 30 degrees and warming in the southern hemisphere.
Rain
Warming increases global average precipitation. Precipitation is when water vapour condenses out of clouds, such as rain and snow. Higher temperatures increase evaporation and surface drying. As the air warms it can hold more water. For every degree Celsius it can hold 7% more water vapour. Scientists have observed changes in the amount, intensity, frequency, and type of precipitation. Overall, climate change is causing longer hot dry spells, broken by more intense rainfall.Climate change has increased contrasts in rainfall amounts between wet and dry seasons. Wet seasons are getting wetter and dry seasons are getting drier. In the northern high latitudes, warming has also caused an increase in the amount of snow and rain. In the Southern Hemisphere, the rain associated with the storm tracks has shifted south. Changes in monsoons vary a lot. More monsoon systems are becoming wetter than drier. In Asia summer monsoons are getting wetter. The West African monsoon is getting wetter over the central Sahel, and drier in the far western Sahel.