But critics say the new push, announced on Thursday, falls short and will allow vast amounts of climate misinformation to slip through the cracks.
Facebook has long been criticized for allowing misinformation about the climate crisis to proliferate on its platform. Mark Zuckerberg, the CEO, admitted in a 2021 April congressional hearing that climate misinformation is "a big issue". In the past, the company has said such misinformation accounts for "a very low percentage of total misinformation on the service" but declined to share figures.
Climate change and misinformation experts have said lies on the platform can spread quickly. The climate denial watchdog groupInfluenceMap in October 2020 found dozens of climate denial ads had been viewed more than 8m times after slipping through the social network's filters.
In March 2021, 13 environmental groups, including the Union of Concerned Scientists and Greenpeace, sent Zuckerberg a letter calling on him to commit to monitoring climate disinformation and provide more transparency about the scale of the problem.
"Climate change disinformation is spreading rapidly across Facebook's social media platform, threatening the ability of citizens and policymakers to fight the climate crisis," the groups wrote.
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.
The largest driver of warming is the emission of gases that create a greenhouse effect, of which more than 90% are carbon dioxide and methane. Fossil fuel burning for energy consumption is the main source of these emissions, with additional contributions from agriculture, deforestation, and manufacturing. The human cause of climate change is not disputed by any scientific body of national or international standing. Temperature rise is accelerated or tempered by climate feedbacks, such as loss of sunlight-reflecting snow and ice cover, increased water vapour , and changes to land and ocean carbon sinks.
Temperature rise on land is about twice the global average increase, leading to desert expansion and more common heat waves and wildfires. Temperature rise is also amplified in the Arctic, where it has contributed to melting permafrost, glacial retreat and sea ice loss. Warmer temperatures are increasing rates of evaporation, causing more intense storms and weather extremes. Impacts on ecosystems include the relocation or extinction of many species as their environment changes, most immediately in coral reefs, mountains, and the Arctic.
Climate change threatens people with food insecurity, water scarcity, flooding, infectious diseases, extreme heat, economic losses, and displacement. These human impacts have led the World Health Organization to call climate change the greatest threat to global health in the 21st century. Even if efforts to minimise future warming are successful, some effects will continue for centuries, including rising sea levels, rising ocean temperatures, and ocean acidification.
Energy flows between space, the atmosphere, and Earth's surface. Rising greenhouse gas levels in the atmosphere are causing a net warming effect to act on Earth's climate system. Many of these impacts are already felt at the current level of warming, which is about 1.2 °C . The Intergovernmental Panel on Climate Change has issued a series of reports that project significant increases in these impacts as warming continues to 1.5 °C and beyond. Additional warming also increases the risk of triggering critical thresholds called tipping points.
Responding to these impacts involves both mitigation and adaptation. Mitigation – limiting climate change – consists of reducing greenhouse gas emissions and removing them from the atmosphere. Methods to achieve this include the development and deployment of low-carbon energy sources such as wind and solar, a phase-out of coal, enhanced energy efficiency, and forest preservation. Adaptation consists of adjusting to actual or expected climate, such as through improved coastline protection, better disaster management, assisted colonisation, and the development of more resistant crops. Adaptation alone cannot avert the risk of 'severe, widespread and irreversible' impacts.
Under the 2015 Paris Agreement, nations collectively agreed to keep warming 'well under 2.0 °C ' through mitigation efforts. However, with pledges made under the Agreement, global warming would still reach about 2.8 °C by the end of the century. Limiting warming to 1.5 °C would require halving emissions by 2030 and achieving near-zero emissions by 2050.
Before the 1980s, when it was unclear whether warming by greenhouse gases would dominate aerosol-induced cooling, scientists often used the term inadvertent climate modification to refer to humankind's impact on the climate. In the 1980s, the terms global warming and climate change were popularised, the former referring only to increased surface warming, the latter describing the full effect of greenhouse gases on the climate. Global warming became the most popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Senate. In the 2000s, the term climate change increased in popularity. Global warming usually refers to human-induced warming of the Earth system, whereas climate change can refer to natural as well as anthropogenic change. The two terms are often used interchangeably.
Various scientists, politicians and media figures have adopted the terms climate crisis or climate emergency to talk about climate change, while using global heating instead of global warming. The policy editor-in-chief of The Guardian explained that they included this language in their editorial guidelines 'to ensure that we are being scientifically precise, while also communicating clearly with readers on this very important issue'. Oxford Dictionary chose climate emergency as its word of the year in 2019 and defines the term as 'a situation in which urgent action is required to reduce or halt climate change and avoid potentially irreversible environmental damage resulting from it'.
Multiple independently produced instrumental datasets show that the climate system is warming, with the 2011–2020 decade being 1.09 °C warmer than the pre-industrial baseline . Surface temperatures are rising by about 0.2 °C per decade, with 2020 reaching a temperature of 1.2 °C above pre-industrial. Since 1950, the number of cold days and nights has decreased, and the number of warm days and nights has increased.
There was little net warming between the 18th century and the mid-19th century. Climate proxies, sources of climate information from natural archives such as trees and ice cores, show that natural variations offset the early effects of the Industrial Revolution. Thermometer records began to provide global coverage around 1850. Historical patterns of warming and cooling, like the Medieval Climate Anomaly and the Little Ice Age, did not occur at the same time across different regions, but temperatures may have reached as high as those of the late-20th century in a limited set of regions. There have been prehistorical episodes of global warming, such as the Paleocene–Eocene Thermal Maximum. However, the modern observed rise in temperature and CO 2 concentrations has been so rapid that even abrupt geophysical events that took place in Earth's history do not approach current rates.
Evidence of warming from air temperature measurements are reinforced with a wide range of other observations. There has been an increase in the frequency and intensity of heavy precipitation, melting of snow and land ice, and increased atmospheric humidity. Flora and fauna are also behaving in a manner consistent with warming; for instance, plants are flowering earlier in spring. Another key indicator is the cooling of the upper atmosphere, which demonstrates that greenhouse gases are trapping heat near the Earth's surface and preventing it from radiating into space.
While locations of warming vary, the patterns are independent of where greenhouse gases are emitted, because the gases persist long enough to diffuse across the planet. Since the pre-industrial period, global average land temperatures have increased almost twice as fast as global average surface temperatures. This is because of the larger heat capacity of oceans, and because oceans lose more heat by evaporation. Over 90% of the additional energy in the climate system over the last 50 years has been stored in the ocean, with the remainder warming the atmosphere, melting ice, and warming the continents.
The Northern Hemisphere and the North Pole have warmed much faster than the South Pole and Southern Hemisphere. The Northern Hemisphere not only has much more land, but also more seasonal snow cover and sea ice, because of how the land masses are arranged around the Arctic Ocean. As these surfaces flip from reflecting a lot of light to being dark after the ice has melted, they start absorbing more heat. Localised black carbon deposits on snow and ice also contribute to Arctic warming. Arctic temperatures have increased and are predicted to continue to increase during this century at over twice the rate of the rest of the world. Melting of glaciers and ice sheets in the Arctic disrupts ocean circulation, including a weakened Gulf Stream, further changing the climate.
The climate system experiences various cycles on its own which can last for years , decades or even centuries. Other changes are caused by an imbalance of energy that is 'external' to the climate system, but not always external to the Earth. Examples of external forcings include changes in the composition of the atmosphere , solar luminosity, volcanic eruptions, and variations in the Earth's orbit around the Sun.
To determine the human contribution to climate change, known internal climate variability and natural external forcings need to be ruled out. A key approach is to determine unique 'fingerprints' for all potential causes, then compare these fingerprints with observed patterns of climate change. For example, solar forcing can be ruled out as a major cause because its fingerprint is warming in the entire atmosphere, and only the lower atmosphere has warmed, as expected from greenhouse gases . Attribution of recent climate change shows that the primary driver is elevated greenhouse gases, but that aerosols also have a strong effect.
The Earth absorbs sunlight, then radiates it as heat. Greenhouse gases in the atmosphere absorb and reemit infrared radiation, slowing the rate at which it can pass through the atmosphere and escape into space. Before the Industrial Revolution, naturally-occurring amounts of greenhouse gases caused the air near the surface to be about 33 °C warmer than it would have been in their absence. While water vapour and clouds are the biggest contributors to the greenhouse effect, they increase as a function of temperature and are therefore considered feedbacks. On the other hand, concentrations of gases such as CO 2 , tropospheric ozone, CFCs and nitrous oxide are not temperature-dependent, and are therefore considered external forcings.
Human activity since the Industrial Revolution, mainly extracting and burning fossil fuels , has increased the amount of greenhouse gases in the atmosphere, resulting in a radiative imbalance. In 2019, the concentrations of CO 2 and methane had increased by about 48% and 160%, respectively, since 1750. These CO 2 levels are higher than they have been at any time during the last 2 million years. Concentrations of methane are far higher than they were over the last 800,000 years.
Global anthropogenic greenhouse gas emissions in 2018, excluding those from land use change, were equivalent to 52 billion tonnes of CO 2. Of these emissions, 72% was actual CO
Despite the contribution of deforestation to greenhouse gas emissions, the Earth's land surface, particularly its forests, remain a significant carbon sink for CO 2. Natural processes, such as carbon fixation in the soil and photosynthesis, more than offset the greenhouse gas contributions from deforestation. The land-surface sink is estimated to remove about 29% of annual global CO 2 emissions. The ocean also serves as a significant carbon sink via a two-step process. First, CO 2 dissolves in the surface water. Afterwards, the ocean's overturning circulation distributes it deep into the ocean's interior, where it accumulates over time as part of the carbon cycle. Over the last two decades, the world's oceans have absorbed 20 to 30% of emitted CO 2.
Aerosols and clouds
Air pollution, in the form of aerosols, not only puts a large burden on human health, but also affects the climate on a large scale. From 1961 to 1990, a gradual reduction in the amount of sunlight reaching the Earth's surface was observed, a phenomenon popularly known as global dimming, typically attributed to aerosols from biofuel and fossil fuel burning. Aerosol removal by precipitation gives tropospheric aerosols an atmospheric lifetime of only about a week, while stratospheric aerosols can remain in the atmosphere for a few years. Globally, aerosols have been declining since 1990, meaning that they no longer mask greenhouse gas warming as much.
In addition to their direct effects , aerosols have indirect effects on the Earth's radiation budget. Sulfate aerosols act as cloud condensation nuclei and thus lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets. This effect also causes droplets to be more uniform in size, which reduces the growth of raindrops and makes clouds more reflective to incoming sunlight. Indirect effects of aerosols are the largest uncertainty in radiative forcing.
While aerosols typically limit global warming by reflecting sunlight, black carbon in soot that falls on snow or ice can contribute to global warming. Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise. Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2 °C by 2050.
Changes of the land surface
Humans change the Earth's surface mainly to create more agricultural land. Today, agriculture takes up 34% of Earth's land area, while 26% is forests, and 30% is uninhabitable . The amount of forested land continues to decrease, largely due to conversion to cropland in the tropics. This deforestation is the most significant aspect of land surface change affecting global warming. The main causes of deforestation are: permanent land-use change from forest to agricultural land producing products such as beef and palm oil , logging to produce forestry/forest products , short term shifting cultivation , and wildfires .
In addition to affecting greenhouse gas concentrations, land-use changes affect global warming through a variety of other chemical and physical mechanisms. Changing the type of vegetation in a region affects the local temperature, by changing how much of the sunlight gets reflected back into space , and how much heat is lost by evaporation. For instance, the change from a dark forest to grassland makes the surface lighter, causing it to reflect more sunlight. Deforestation can also contribute to changing temperatures by affecting the release of aerosols and other chemical compounds that influence clouds, and by changing wind patterns. In tropic and temperate areas the net effect is to produce significant warming, while at latitudes closer to the poles a gain of albedo leads to an overall cooling effect. Globally, these effects are estimated to have led to a slight cooling, dominated by an increase in surface albedo.
Solar and volcanic activity
Physical climate models are unable to reproduce the rapid warming observed in recent decades when taking into account only variations in solar output and volcanic activity. As the Sun is the Earth's primary energy source, changes in incoming sunlight directly affect the climate system. Solar irradiance has been measured directly by satellites, and indirect measurements are available from the early 1600s. There has been no upward trend in the amount of the Sun's energy reaching the Earth. Further evidence for greenhouse gases being the cause of recent climate change come from measurements showing the warming of the lower atmosphere , coupled with the cooling of the upper atmosphere . If solar variations were responsible for the observed warming, warming of both the troposphere and the stratosphere would be expected, but that has not been the case.
Explosive volcanic eruptions represent the largest natural forcing over the industrial era. When the eruption is sufficiently strong sunlight can be partially blocked for a couple of years, with a temperature signal lasting about twice as long. In the industrial era, volcanic activity has had negligible impacts on global temperature trends. Present-day volcanic CO2 emissions are equivalent to less than 1% of current anthropogenic CO2 emissions.