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 would require halving emissions by 2030 and achieving net-zero emissions by 2050.
John Tyndall's ratio spectrophotometer (drawing from 1861) measured how much infrared radiation was absorbed and emitted by various gases filling its central tube. Such measurements furthered understanding of the greenhouse effect that underlies global warming and climate change.
The history of the scientific discovery of climate change began in the early 19th century when ice ages and other natural changes in paleoclimate were first suspected and the natural greenhouse effect was first identified. In the late 19th century, scientists first argued that human emissions of greenhouse gases could change Earth's energy balance and climate. The existence of the greenhouse effect, while not named as such, was proposed as early as 1824 by Joseph Fourier. The argument and the evidence were further strengthened by Claude Pouillet in 1827 and 1838. In 1856 Eunice Newton Foote demonstrated that the warming effect of the sun is greater for air with water vapour than for dry air, and the effect is even greater with carbon dioxide.
John Tyndall was the first to measure the infrared absorption and emission of various gases and vapors. From 1859 onwards, he showed that the effect was due to a very small proportion of the atmosphere, with the main gases having no effect, and was largely due to water vapor, though small percentages of hydrocarbons and carbon dioxide had a significant effect. The effect was more fully quantified by Svante Arrhenius in 1896, who made the first quantitative prediction of global warming due to a hypothetical doubling of atmospheric carbon dioxide.
In the 1960s, the evidence for the warming effect of carbon dioxide gas became increasingly convincing. Scientists also discovered that human activities that generated atmospheric aerosols (e.g., "air pollution") could have cooling effects as well (later referred to as global dimming). Other theories for the causes of global warming were also proposed, involving forces from volcanism to solar variation. During the 1970s, scientific understanding of global warming greatly increased. (Full article...)
An image of the Earth's cloud cover, which is the amount of sky obscured by clouds, based largely on observations from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Terra satellite. Clouds play multiple critical roles in the climate system. In particular, being bright objects in the visible part of sunlight, they efficiently reflect light to space and thus contribute to the cooling of the planet.
She was the longest-serving administrator in the history of the EPA, staying through both terms of the Clinton presidency. During her tenure, she reorganized the agency's enforcement structure and oversaw two new programs designed to create flexible partnerships with industry as an alternative to traditional regulation. She started a successful program to deal with contaminated lands in urban areas. She took the lead within the administration in defending existing environmental laws and budgets and was the driving force behind a stringent tightening of air quality standards that led to a prolonged political and legal battle. (Full article...)
Image 2Carbon 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 4Since 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 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 6Meat from cattle and sheep have the highest emissions intensity of any agricultural commodity. (from Causes of climate change)
Image 9CO2 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 10Observed 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 11The 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 12Erratics, 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 13Earth'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 14Cumulative land-use change contributions to CO2 emissions, by region. (from Causes of climate change)
Image 17Atmospheric 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 21This diagram of the 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 23Modeled 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 24A 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)
Image 25Drivers of climate change from 1850–1900 to 2010–2019. Future global warming potential for long lived drivers like carbon dioxide emissions is not represented. (from Causes of climate change)
Image 27Earth'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 28Air 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 30A diagram which shows where the extra heat retained on Earth due to the energy imbalance is going. (from Causes of climate change)
Image 31Annual 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 33The 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 34Greenhouse 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 36Mean 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 37CO2 concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black) (from Causes of climate change)
Image 38Sea 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 39The 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 41Schematic drawing of Earth's excess heat inventory and energy imbalance for two recent time periods. (from Earth's energy budget)
Image 42Between 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 43Scientific 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 44The 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 50Energy 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 51Over 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 53Terms 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 55Warming 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 56Global 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)
Sea level trends between 1993 and 2010. Per the U.S. National Oceanic and Atmospheric Administration (NOAA), "The following maps provide estimates of sea level rise based on measurements from satellite radar altimeters. The local trends were estimated using data from TOPEX/Poseidon (T/P), Jason-1, and Jason-2, which have monitored the same ground track since 1992.
An inverted barometer has been applied. The estimates of sea level rise do not include glacial isostatic adjustment effects on the geoid, which are modeled to be +0.2 to +0.5 mm/year when globally averaged."
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