Many climate change impacts have been felt in recent years, with 2023 the warmest on record at +1.48 °C (2.66 °F) since regular tracking began in 1850. Additional warming will increase these impacts and can trigger tipping points, such as melting all of the Greenland ice sheet. Under the 2015 Paris Agreement, nations collectively agreed to keep warming "well under 2 °C". However, with pledges made under the Agreement, global warming would still reach about 2.7 °C (4.9 °F) by the end of the century. Limiting warming to 1.5 °C will require halving emissions by 2030 and achieving net-zero emissions by 2050.
Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. What distinguishes them from other gases is that they absorb the wavelengths of radiation that a planet emits, resulting in the greenhouse effect. The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. Without greenhouse gases in the atmosphere, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F).
Carbon dioxide is causing about three-quarters of global warming and can take thousands of years to be fully absorbed by the carbon cycle. Methane causes most of the remaining warming and lasts in the atmosphere for an average of 12 years. Human activities since the beginning of the Industrial Revolution (around 1750) have increased carbon dioxide by over 50%, up to a level not seen in over 3 million years. The atmospheric methane concentrations have increased by over 150% during the same time period. (Full article...)
Image 2Mean temperature anomalies during the period 1965 to 1975 with respect to the average temperatures from 1937 to 1946. This dataset was not available at the time. (from History of climate change science)
Image 3Global average temperatures show that the Medieval Warm Period was not a planet-wide phenomenon, and that the Little Ice Age was not a distinct planet-wide time period but rather the end of a long temperature decline that preceded recent global warming. (from Temperature record of the last 2,000 years)
Image 4Earth's energy balance and imbalance, showing where the excess energy goes: Outgoing radiation is decreasing owing to increasing greenhouse gases in the atmosphere, leading to Earth's energy imbalance of about 460 TW. The percentage going into each domain of the climate system is also indicated. (from Earth's energy budget)
Image 5CO2 sources and sinks since 1880. While there is little debate that excess carbon dioxide in the industrial era has mostly come from burning fossil fuels, the future strength of land and ocean carbon sinks is an area of study. (from Causes of climate change)
Image 6CO2 concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black) (from Causes of climate change)
Image 8Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar. (from Carbon dioxide in Earth's atmosphere)
Image 9Schematic drawing of Earth's excess heat inventory and energy imbalance for two recent time periods. (from Earth's energy budget)
Image 10Modeled simulation of the effect of various factors (including GHGs, Solar irradiance) singly and in combination, showing in particular that solar activity produces a small and nearly uniform warming, unlike what is observed. (from History of climate change science)
Image 12Over 400,000 years of ice core data: Graph of CO2 (green), reconstructed temperature (blue) and dust (red) from the Vostok ice core (from Carbon dioxide in Earth's atmosphere)
Image 14The growth in Earth's energy imbalance from satellite and in situ measurements (2005–2019). A rate of +1.0 W/m2 summed over the planet's surface equates to a continuous heat uptake of about 500 terawatts (~0.3% of the incident solar radiation). (from Earth's energy budget)
Image 15A diagram which shows where the extra heat retained on Earth due to the energy imbalance is going. (from Causes of climate change)
Image 16The impact of the greenhouse effect on climate was presented to the public early in the 20th century, as succinctly described in this 1912 Popular Mechanics article. (from History of climate change science)
Image 17Between 1850 and 2019 the Global Carbon Project estimates that about 2/3rds of excess carbon dioxide emissions have been caused by burning fossil fuels, and a little less than half of that has stayed in the atmosphere. (from Carbon dioxide in Earth's atmosphere)
Image 19Observed temperature from NASA vs the 1850–1900 average used by the IPCC as a pre-industrial baseline. The primary driver for increased global temperatures in the industrial era is human activity, with natural forces adding variability. (from Causes of climate change)
Image 20Carbon dioxide observations from 2008 to 2017 showing the seasonal variations and the difference between northern and southern hemispheres (from Carbon dioxide in Earth's atmosphere)
Image 22Annual CO2 flows from anthropogenic sources (left) into Earth's atmosphere, land, and ocean sinks (right) since year 1960. Units in equivalent gigatonnes carbon per year. (from Carbon dioxide in Earth's atmosphere)
Image 25Terms like "climate emergency" and climate crisis" have often been used by activists, and are increasingly found in academic papers. (from History of climate change science)
Image 27This diagram of the fast carbon cycle shows the movement of carbon between land, atmosphere, and oceans in billions of metric tons of carbon per year. Yellow numbers are natural fluxes, red are human contributions, white are stored carbon. (from Carbon dioxide in Earth's atmosphere)
Image 28Erratics, boulders deposited by glaciers far from any existing glaciers, led geologists to the conclusion that climate had changed in the past. (from History of climate change science)
Image 29Cumulative land-use change contributions to CO2 emissions, by region. (from Causes of climate change)
Image 31Sea 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. (from Causes of climate change)
Image 32Warming influence of atmospheric greenhouse gases has nearly doubled since 1979, with carbon dioxide and methane being the dominant drivers. (from Causes of climate change)
Image 34Energy flows between space, the atmosphere, and Earth's surface. Rising greenhouse gas levels are contributing to an energy imbalance. (from Causes of climate change)
Image 37The rising accumulation of energy in the oceanic, land, ice, and atmospheric components of Earth's climate system since 1960. (from Earth's energy budget)
Image 39CO2 reduces the flux of thermal radiation emitted to space (causing the large dip near 667 cm−1), thereby contributing to the greenhouse effect. (from Carbon dioxide in Earth's atmosphere)
Image 42Earth's energy budget (in W/m2) determines the climate. It is the balance of incoming and outgoing radiation and can be measured by satellites. The Earth's energy imbalance is the "net absorbed" energy amount and grew from +0.6 W/m2 (2009 est.) to above +1.0 W/m2 in 2019. (from Earth's energy budget)
Image 43Greenhouse gases allow sunlight to pass through the atmosphere, heating the planet, but then absorb and redirect the infrared radiation (heat) the planet emits (from Carbon dioxide in Earth's atmosphere)
Image 46Atmospheric CO2 concentration measured at Mauna Loa Observatory in Hawaii from 1958 to 2023 (also called the Keeling Curve). The rise in CO2 over that time period is clearly visible. The concentration is expressed as μmole per mole, or ppm. (from Carbon dioxide in Earth's atmosphere)
Image 47Since the 1980s, global average surface temperatures during a given decade have almost always been higher than the average temperature in the preceding decade. (from History of climate change science)
Image 48Drivers of climate change from 1850–1900 to 2010–2019. There was no significant contribution from internal variability or solar and volcanic drivers. (from Causes of climate change)
Image 49The US, China and Russia have cumulatively contributed the greatest amounts of CO2 since 1850. (from Carbon dioxide in Earth's atmosphere)
Image 50Scientific 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. A 2019 study found scientific consensus to be at 100%, and a 2021 study concluded that consensus exceeded 99%. Another 2021 study found that 98.7% of climate experts indicated that the Earth is getting warmer mostly because of human activity. (from History of climate change science)
Image 51The rate of global tree cover loss has approximately doubled since 2001, to an annual loss approaching an area the size of Italy. (from Causes of climate change)
Image 52Meat from cattle and sheep have the highest emissions intensity of any agricultural commodity. (from Causes of climate change)
Image 54Air pollution has substantially increased the presence of aerosols in the atmosphere when compared to the preindustrial background levels. Different types of particles have different effects, but overall, cooling from aerosols formed by sulfur dioxide emissions has the overwhelming impact. However, the complexity of aerosol interactions in atmospheric layers makes the exact strength of cooling very difficult to estimate. (from Causes of climate change)
Image 56A Sankey diagram illustrating a balanced example of Earth's energy budget. Line thickness is linearly proportional to relative amount of energy. (from Earth's energy budget)
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