Global Warming and Its Effects

 

The phenomenon of rising average air temperatures close to the surface of the Earth over the previous one to two centuries is known as global warming. Since the middle of the 20th century, climate scientists have accumulated extensive data on a variety of weather events, including temperatures, precipitation, and storms, as well as on factors that have an impact on climate, such as ocean currents and the chemical makeup of the atmosphere. 

These findings show that Earth's climate has changed on practically every possible period since the beginning of geologic time and that human activities have increasingly affected the pace and scope of current climate change since the beginning of the Industrial Revolution.

 

The World Meteorological Organization (WMO) and the United Nations Environment Program established the Intergovernmental Panel on Climate Change (IPCC) in 1988 to give voice to a growing belief held by the majority of scientists (UNEP). The increase in global average surface temperature between 1850 and 2019 was best estimated to have increased by 1.07 °C (1.9 °F), according to the IPCC's Sixth Assessment Report (AR6), which was released in 2021. The majority of the warming over the second half of the 20th century could be attributed to human activities, according to an IPCC special report published in 2018. It noted that humans and their activities have been responsible for a worldwide average temperature increase between 0.8 and 1.2 °C (1.4 and 2.2 °F) since preindustrial times.

 

Climatic variation since the last glaciation

The more widespread phenomena of climate change, which denotes modifications to the full range of characteristics that characterise climate, is tied to global warming. Climate change affects not only changes in air temperature but also in wind patterns, ocean currents, and other aspects of Earth's climate. Typically, one can think of climate change as the result of a variety of natural processes acting on the planet over a range of timescales. Since the beginning of human civilization, there has been a "anthropogenic," or solely human-caused, component to climate change, and this anthropogenic component has grown in significance over the past two centuries during the industrial era. Any warming of the near-surface air over the past 200 years that can be linked to human activity is particularly referred to as global warming.

 

Causes of global warming

The greenhouse effect

Different types of solar and terrestrial radiation are kept in balance to keep the Earth's average surface temperature constant. Because the frequencies of the radiation are extremely high and the wavelengths are relatively short—not far from the visible region of the electromagnetic spectrum—solar radiation is frequently referred to as "shortwave" radiation. Terrestrial radiation, on the other hand, is frequently referred to as "longwave" radiation due to the comparatively low frequencies and lengthy wavelengths—somewhere in the infrared region of the spectrum. Watts per square metre are commonly used to assess downward-moving solar energy. The "solar constant," or total solar radiation energy, is equal to around 1,366 watts per square metre per year at the top of the Earth's atmosphere. Adjusting for the fact that only one-half of the planet’s surface receives solar radiation at any given time, the average surface insolation is 342 watts per square metre annually.

Only a small portion of the total solar radiation that enters the atmosphere is absorbed by the Earth's surface. Approximately 30 units of the incoming solar radiation for every 100 are reflected back to space by the atmosphere, the clouds, or reflecting areas of the Earth's surface. The spatial breadth and distribution of reflective structures, such as clouds and ice cover, can fluctuate, which means that Earth's global albedo need not remain constant over time. The atmosphere, clouds, or surface may absorb the 70 solar energy units that are not reflected. Earth's surface and atmosphere must emit these same 70 radiations in order to preserve thermodynamic equilibrium in the absence of further problems. Earth’s surface temperature (and that of the lower layer of the atmosphere essentially in contact with the surface) is tied to the magnitude of this emission of outgoing radiation according to the Stefan-Boltzmann law.

 

The influences of human activity on climate

 

Greenhouse gases

 

By increasing the net downward longwave radiation that reaches the surface, greenhouse gases, as mentioned above, warm the Earth's surface. Each greenhouse gas has a unique correlation between atmospheric concentration and the surface-related positive radiative forcing. Each greenhouse gas has unique chemical characteristics that affect how much longwave radiation it can absorb on a relative basis. The radiative properties of each significant greenhouse gas are discussed in the paragraphs that follow.

 

The most powerful greenhouse gas in the Earth's atmosphere is water vapour, yet it behaves very differently from the other greenhouse gases. Instead of acting as a direct radiative forcing agent, water vapor's main function in the climate system is as a climate feedback, or a reaction that affects the system's continuous operation (see below Water vapour feedback). This discrepancy results from the fact that air temperatures, rather than human behaviour, generally cannot directly alter the amount of water vapour in the atmosphere. The rate at which water evaporates from a surface increases with surface temperature.

Carbon dioxide

 

Carbon dioxide (CO2) is the most significant of the greenhouse gases. Outgassing from volcanoes, the burning and organic matter's natural decomposition, and aerobic organisms' respiration are all examples of natural sources of atmospheric CO2. These sources are typically counterbalanced by a collection of "sinks"—a collection of physical, chemical, or biological processes—that function to remove CO2 from the atmosphere. Terrestrial vegetation, which absorbs CO2 through photosynthesis, is one of the main natural sinks.

 

Recognize how the atmosphere's carbon and oxygen cycles work.

Also serving as carbon sinks are a number of oceanic processes. The "solubility pump," one of these procedures, entails the descent of surface seawater containing dissolved CO2. The "biological pump," a different mechanism, involves the uptake of dissolved CO2 by marine vegetation, phytoplankton (small, free-floating photosynthetic organisms), or other marine animals that use CO2 to create calcium carbonate skeletons and other structures (CaCO3). The carbon these organisms possess is carried downward and eventually buried at deep as they perish and sink to the ocean floor.

 

In contrast, burning fossil fuels—primarily coal and oil, and secondarily natural gas—for transportation, heating, and the creation of electricity, as well as the manufacture of cement, are the main ways that human activities raise atmospheric CO2 levels. The burning of forests and the clearing of land are examples of additional anthropogenic sources. Currently, anthropogenic emissions are responsible for around 7 gigatonnes (7 billion tonnes) of carbon dioxide entering the atmosphere each year. Anthropogenic emissions make up about 3% of all CO2 emissions from all natural sources, and they are significantly greater than the capacity of natural sinks to offset them (by perhaps as much as 2–3 gigatons per year).

 

As a result, from 1959 and 2006, CO2 accumulated in the atmosphere at an average rate of 1.4 ppm per year and about 2.0 ppm per year from 2006 to 2018. This rate of accumulation has generally been linear (that is, uniform over time). But in the future, certain current sinks, like the oceans, might turn into sources (see Carbon cycle feedbacks). This could result in a scenario where the atmospheric CO2 content increases at an exponential pace (that is, its rate of increase is also increasing).

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