Many climate change impacts have been observed in the first decades of the 21st century, with 2024 the warmest on record at +1.60°C (2.88°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 2.8°C (5.0°F) by the end of the century.
The United Nations Framework Convention on Climate Change (UNFCCC) is the UN process for negotiating an agreement to limit dangerous climate change. It is an international treaty among countries to combat "dangerous human interference with the climate system". The main way to do this is limiting the increase in greenhouse gases in the atmosphere. The Convention established the principle of "common but differentiated responsibilities," which asserts that all countries share responsibility for addressing climate change. However, developed countries are expected to assume a leading role because of their greater historical emissions. It was signed in 1992 by 154 states at the UN Conference on Environment and Development (UNCED), known as the Earth Summit. The treaty entered into force in 1994. "UNFCCC" is also the name of the Secretariat charged with supporting the operation of the convention, with offices on the UN Campus in Bonn, Germany.
The treaty calls for continuing scientific research into the climate. This research supports meetings and negotiations to lead to agreements. The aim is to allow ecosystems to adapt to climate change. At the same time it aims to ensure there are no threats to food production from climate change or measures to address it. And it aims to enable economic development to proceed in a sustainable manner. The UNFCCC's work currently focuses on implementing the Paris Agreement, which entered into force in 2016. It aims to limit the rise in global temperature to well below 2°C (3.6°F) above levels before the Industrial Revolution, and even aiming to hold it at 1.5°C (2.7°F). The treaty sets out responsibilities for three categories of states: developed countries, developed countries with special financial responsibilities, and developing countries. The developed countries are called Annex I countries, and should adopt national policies and take corresponding measures to limit their emissions of greenhouse gases. They should report on steps for returning individually or jointly to their 1990 greenhouse gas emission levels.
By 2022, the UNFCCC had 198 parties. Its supreme decision-making body, the Conference of the Parties (COP), meets annually. Other meetings at the regional and technical level take place throughout the year. The Paris Agreement mandates a review or "global stocktake" of progress towards meeting its goals every five years. The first of these took place at COP28 in the United Arab Emirates (UAE) in 2023. (Full article...)
Image 2The 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 4Erratics, 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 8Terms 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 9Cumulative land-use change contributions to CO2 emissions, by region. (from Causes of climate change)
Image 10Human fingerprints for global warming (summary of observational evidence that human carbon dioxide emissions are causing the climate to warm). (from Causes of climate change)
Image 11Earth's energy imbalance has increased in the 21st century, reaching values twice that of prior estimates from the IPCC. The ability to observe this imbalance is deteriorating because satellites are being decommissioned. (from Earth's energy budget)
Image 15This 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 the atmosphere of Earth)
Image 17Scientific 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 18CO2 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 19Air 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 22CO2 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 the atmosphere of Earth)
Image 23The 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 24Earth'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. (from Earth's energy budget)
Image 26The growth in Earth's energy imbalance from satellite and in situ measurements (2005–2019). A rate of +1.0W/m2 summed over the planet's surface equates to a continuous heat uptake of about 500terawatts (~0.3% of the incident solar radiation). (from Earth's energy budget)
Image 32Meat from cattle and sheep have the highest emissions intensity of any agricultural commodity. (from Causes of climate change)
Image 33Greenhouse 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 the atmosphere of Earth)
Image 34Sea 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 36The 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 38Between 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 the atmosphere of Earth)
Image 39Since 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 42Annual 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 the atmosphere of Earth)
Image 43A 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 44Earth'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 45Mean 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 46Schematic drawing of Earth's excess heat inventory and energy imbalance for two recent time periods (from Earth's energy budget)
Image 47Carbon dioxide observations from 2008 to 2017 showing the seasonal variations and the difference between northern and southern hemispheres (from Carbon dioxide in the atmosphere of Earth)
Image 49Global 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 50Extreme event attribution methods generally involve applying climate change models to scenarios in both the "real" world that is experiencing global warming, and a simulated world that does not suffer the drivers of global warming. Differences between the results of the two processes—especially the frequency, intensity and impacts of extreme weather events—are then analyzed to arrive at the attribution result. (from History of climate change science)
Plant Productivity in a Warming World: The past decade is the warmest on record since instrumental measurements began in the 1880s. Previous research suggested that in the '80s and '90s, warmer global temperatures and higher levels of precipitation—factors associated with climate change—were generally good for plant productivity. An updated analysis published this week in Science indicates that as temperatures have continued to rise, the benefits to plants are now overwhelmed by longer and more frequent droughts. High-resolution data from the Moderate-Resolution Imaging Spectroradiometer, or MODIS, indicate a net decrease in net primary production (NPP) from 2000-2009, as compared to the previous two decades. This narrated video gives an overview of NPP and the carbon cycle.
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