Climate change

Carbon dioxide, the primary gas driving global warming, has increased in concentration by about 50% since the pre-industrial era to levels not seen for millions of years.

[62] This is why the temperature change is defined in terms of a 20-year average, which reduces the noise of hot and cold years and decadal climate patterns, and detects the long-term signal.

[78][79][80] Melting of ice sheets near the poles weakens both the Atlantic and the Antarctic limb of thermohaline circulation, which further changes the distribution of heat and precipitation around the globe.

[97] Examples of these include changes in the concentrations of greenhouse gases, solar luminosity, volcanic eruptions, and variations in the Earth's orbit around the Sun.

[105][106] Human activity since the Industrial Revolution, mainly extracting and burning fossil fuels (coal, oil, and natural gas),[107] has increased the amount of greenhouse gases in the atmosphere.

[112][113][114][115] Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, and coal mining, as well as oil and gas extraction.

While plants on land and in the ocean absorb most excess emissions of CO2 every year, that CO2 is returned to the atmosphere when biological matter is digested, burns, or decays.

[130] In tropic and temperate areas the net effect is to produce significant warming, and forest restoration can make local temperatures cooler.

[142] The effect of decreasing sulfur content of fuel oil for ships since 2020[143] is estimated to cause an additional 0.05 °C increase in global mean temperature by 2050.

[195] Marine ice sheet instability processes in Antarctica may add substantially to these values,[196] including the possibility of a 2-meter sea level rise by 2100 under high emissions.

[202] Greater degrees of global warming increase the risk of passing through 'tipping points'—thresholds beyond which certain major impacts can no longer be avoided even if temperatures return to their previous state.

The collapse of major ocean currents like the Atlantic meridional overturning circulation (AMOC), and irreversible damage to key ecosystems like the Amazon rainforest and coral reefs can unfold in a matter of decades.

[212] Further, the West Antarctic ice sheet appears committed to practically irreversible melting, which would increase the sea levels by at least 3.3 m (10 ft 10 in) over approximately 2000 years.

[222] Just as on land, heat waves in the ocean occur more frequently due to climate change, harming a wide range of organisms such as corals, kelp, and seabirds.

[224] Harmful algal blooms enhanced by climate change and eutrophication lower oxygen levels, disrupt food webs and cause great loss of marine life.

[256] An expert elicitation concluded that the role of climate change in armed conflict has been small compared to factors such as socio-economic inequality and state capabilities.

[272] The United Nations Environment Programme estimates that countries need to triple their pledges under the Paris Agreement within the next decade to limit global warming to 2 °C.

[273] With pledges made under the Paris Agreement as of 2024, there would be a 66% chance that global warming is kept under 2.8 °C by the end of the century (range: 1.9–3.7 °C, depending on exact implementation and technological progress).

[289] While solar panels and onshore wind are now among the cheapest forms of adding new power generation capacity in many locations,[290] green energy policies are needed to achieve a rapid transition from fossil fuels to renewables.

[302] Low-carbon energy improves human health by minimizing climate change as well as reducing air pollution deaths,[303] which were estimated at 7 million annually in 2016.

In these industries, carbon-intensive materials such as coke and lime play an integral role in the production, so that reducing CO2 emissions requires research into alternative chemistries.

[334] The first two decades of the 21st century saw an increase in adaptive capacity in most low- and middle-income countries with improved access to basic sanitation and electricity, but progress is slow.

[337] In agriculture, adaptation options include a switch to more sustainable diets, diversification, erosion control, and genetic improvements for increased tolerance to a changing climate.

[360] Production of emissions is another way to look at responsibility: under that approach, the top 21 fossil fuel companies would owe cumulative climate reparations of $5.4 trillion over the period 2025–2050.

[365] As stated in the convention, this requires that greenhouse gas concentrations are stabilized in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and economic development can be sustained.

[373] The Accord set the goal of sending $100 billion per year to developing countries for mitigation and adaptation by 2020, and proposed the founding of the Green Climate Fund.

[394] As of 2021, based on information from 48 national climate plans, which represent 40% of the parties to the Paris Agreement, estimated total greenhouse gas emissions will be 0.5% lower compared to 2010 levels, below the 45% or 25% reduction goals to limit global warming to 1.5 °C or 2 °C, respectively.

[413] Concern has increased over time,[414] and a majority of citizens in many countries now express a high level of worry about climate change, or view it as a global emergency.

Activists also initiate lawsuits which target governments and demand that they take ambitious action or enforce existing laws on climate change.

She concluded that "An atmosphere of that gas would give to our earth a high temperature..."[428][429] Starting in 1859,[430] John Tyndall established that nitrogen and oxygen—together totalling 99% of dry air—are transparent to radiated heat.

The global map shows sea temperature rises of 0.5 to 1 degree Celsius; land temperature rises of 1 to 2 degrees Celsius; and Arctic temperature rises of up to 4 degrees Celsius.
Changes in surface air temperature over the past 50 years. [ 1 ] The Arctic has warmed the most, and temperatures on land have generally increased more than sea surface temperatures .
Earth's average surface air temperature has increased almost 1.5 °C (about 2.5 °F) since the Industrial Revolution . Natural forces cause some variability, but the 20-year average shows the progressive influence of human activity. [ 2 ]
Global surface temperature reconstruction over the last 2000 years using proxy data from tree rings, corals, and ice cores in blue. [ 38 ] Directly observed data is in red. [ 39 ]
In recent decades, new high temperature records have substantially outpaced new low temperature records on a growing portion of Earth's surface. [ 48 ]
There has been an increase in ocean heat content during recent decades as the oceans absorb over 90% of the heat from global warming . [ 49 ]
NASA animation portraying global surface temperature changes from 1880 to 2023. The colour blue denotes cooler temperatures and red denotes warmer temperatures.
CMIP6 multi-model projections of global surface temperature changes for the year 2090 relative to the 1850–1900 average. The current trajectory for warming by the end of the century is roughly halfway between these two extremes. [ 22 ] [ 85 ] [ 86 ]
Physical drivers of global warming that has happened so far. Future global warming potential for long lived drivers like carbon dioxide emissions is not represented. Whiskers on each bar show the possible error range .
CO 2 concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black)
The Global Carbon Project shows how additions to CO 2 since 1880 have been caused by different sources ramping up one after another.
The rate of global tree cover loss has approximately doubled since 2001, to an annual loss approaching an area the size of Italy. [ 124 ]
The Fourth National Climate Assessment ("NCA4", USGCRP, 2017) includes charts illustrating that neither solar nor volcanic activity can explain the observed warming. [ 145 ] [ 146 ]
Sea ice reflects 50% to 70% of incoming sunlight, while the ocean, being darker, reflects only 6%. As an area of sea ice melts and exposes more ocean, more heat is absorbed by the ocean, raising temperatures that melt still more ice. This is a positive feedback process . [ 153 ]
Energy flows between space, the atmosphere, and Earth's surface. Most sunlight passes through the atmosphere to heat the Earth's surface, then greenhouse gases absorb most of the heat the Earth radiates in response. Adding to greenhouse gases increases this insulating effect, causing an energy imbalance that heats the planet up.
The sixth IPCC Assessment Report projects changes in average soil moisture at 2.0 °C of warming, as measured in standard deviations from the 1850 to 1900 baseline.
Historical sea level reconstruction and projections up to 2100 published in 2017 by the U.S. Global Change Research Program [ 193 ]
Different levels of global warming may cause different parts of Earth's climate system to reach tipping points that cause transitions to different states. [ 203 ] [ 204 ]
Extreme weather will be progressively more common as the Earth warms. [ 232 ]
Global greenhouse gas emission scenarios, based on policies and pledges as of November 2021
Coal, oil, and natural gas remain the primary global energy sources even as renewables have begun rapidly increasing. [ 283 ]
Wind and solar power, Germany
Taking into account direct and indirect emissions, industry is the sector with the highest share of global emissions. Data as of 2019 from the IPCC.
Most CO 2 emissions have been absorbed by carbon sinks , including plant growth, soil uptake, and ocean uptake ( 2020 Global Carbon Budget ).
The Climate Change Performance Index ranks countries by greenhouse gas emissions (40% of score), renewable energy (20%), energy use (20%), and climate policy (20%).
High
Medium
Low
Very low
Since 2000, rising CO 2 emissions in China and the rest of world have surpassed the output of the United States and Europe. [ 363 ]
Per person, the United States generates CO 2 at a far faster rate than other primary regions. [ 363 ]
Annual CO 2 emissions by region . This measures fossil fuel and industry emissions. Land use change is not included. [ 386 ]
Data has been cherry picked from short periods to falsely assert that global temperatures are not rising. Blue trendlines show short periods that mask longer-term warming trends (red trendlines). Blue rectangle with blue dots shows the so-called global warming hiatus . [ 396 ]
The public substantially underestimates the degree of scientific consensus that humans are causing climate change. [ 404 ] Studies from 2019 to 2021 [ 405 ] [ 4 ] [ 406 ] found scientific consensus to range from 98.7 to 100%.
This 1912 article succinctly describes the greenhouse effect, how burning coal creates carbon dioxide to cause global warming and climate change. [ 422 ]
Studying what would become known as the greenhouse effect, Tyndall's pre-1861 ratio spectrophotometer measured how much various gases in a tube absorb and emit infrared radiation—which humans experience as heat.
Scientific consensus on causation: Academic studies of scientific agreement on human-caused global warming among climate experts (2010–2015) reflect that the level of consensus correlates with expertise in climate science. [ 435 ] A 2019 study found scientific consensus to be at 100%, [ 436 ] and a 2021 study concluded that consensus exceeded 99%. [ 437 ] Another 2021 study found that 98.7% of climate experts indicated that the Earth is getting warmer mostly because of human activity. [ 438 ]