Impact of Global Warming
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 various weather events, including temperatures, precipitation, and storms, as well as on factors that impact climates, such as ocean currents and the chemical makeup of the atmosphere. These findings show that Earth's climate has changed in 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 global average surface temperature increase 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), 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.
AR6 generated several global climate forecasts based on the simulation of five greenhouse gas emission scenarios that took into consideration present-day emissions, future emissions, mitigation (severity reduction) strategies, and projection uncertainties. The precise function of feedback mechanisms and the effects of the industrial pollutants known as aerosols, which may partially counterbalance warming, are some of the biggest uncertainties. According to the lowest-emissions scenario, which presupposed significant reductions in greenhouse gas emissions starting in 2015, the average global surface temperature would rise between 1.0 and 1.8 °C (1.8 and 3.2 °F) by 2100 in comparison to the average between 1850 and 1900.
This range contrasted sharply with the highest-emissions scenario, which assumed that greenhouse gas emissions would continue to climb throughout the 21st century and projected that the mean surface temperature would rise between 3.3 and 5.7 °C (5.9 and 10.2 °F) by 2100. The intermediate-emissions scenario predicted an increase of between 2.1 and 3.5 °C (3.8 and 6.3 °F) by 2100, assuming that emissions would stabilize by 2050 and then steadily decline.
Global Warming Effects
Many climate experts concur that if the global average temperature increased by more than 2 °C (3.6 °F) in such a short period, serious societal, economic, and ecological harm would follow. Increased extinction rates of several plant and animal species, changes in agricultural practices, and increasing sea levels are only a few examples of this kind of harm. By the Paris Agreement, which aims to assist nations in limiting global warming to 1.5 °C (2.7 °F) above preindustrial levels to avoid the worst predicted effects, all national governments, except a few, had started the process of implementing carbon reduction plans by 2015.
The average near-surface air temperature will rise by 1.5 °C sometime between 2030 and 2052, according to the authors of the 2018 special report, whereas the authors of the AR6 report predicted that this threshold would be achieved by 2041 at the latest.
The AR6 report also observed that between 1901 and 2018, the average worldwide sea level rose by about 20 cm (7.9 inches) and that the second half of the 20th century had a greater increase in sea level than the first. Additionally, it estimated that again depending on a wide variety of scenarios, the average worldwide sea level would rise by varying amounts by 2100 in comparison to the average between 1995 and 2014. Sea level would rise by 28–55 cm (11.1–21.7 inches) under the report's lowest emission scenario, whereas it would rise by 44–76 cm (17.3-29.9 inches) under the report's intermediate emission scenario. According to the scenario with the highest emissions, the sea level would rise by 63–101 cm (24.8–39.8 inches) by the year 2100.
The aforementioned possibilities mostly depend on future quantities of specific trace gases, often known as greenhouse gases, which have been steadily introduced into the lower atmosphere through the combustion of fossil fuels for transportation, industry, and household purposes. The so-called greenhouse effect, which causes the Earth's surface and lower atmosphere to warm due to the presence of water vapor, carbon dioxide, methane, nitrous oxides, and other greenhouse gases, has grown in intensity, which is the cause of modern global warming. The first time that atmospheric levels of carbon dioxide, methane, and nitrous oxide exceeded those observed in ice cores extending back 800,000 years was reported by the IPCC in 2014.
The most significant of these gases is carbon dioxide, which contributes to both the greenhouse effect and the global economy. It has been calculated that the atmospheric carbon dioxide concentrations were around 280 parts per million at the start of the industrial age in the middle of the 18th century (ppm). They increased to 416 ppm by the end of 2021, and if fossil fuels are consumed at the current rate, it is predicted that they will reach 550 ppm by the middle of the 21st century, or a doubling of carbon dioxide concentrations in 300 years.
The magnitude and significance of rising surface temperatures, the impacts of past and future warming on human life, and the necessity of taking action to mitigate future warming and deal with its effects are all topics of intense debate. An overview of the scientific literature and current public policy discussions on the topic of global warming is given in this article. It examines the elements that contribute to rising near-surface air temperatures, the methods used in climate research and forecasting, potential biological and social effects of rising temperatures, and changes in public policy since the middle of the 20th century. See climate for a thorough explanation of the Earth's climate, its mechanisms, and how living things adapt to it.
Climatic Variation Since the Last Glaciation of Global Warming
The more widespread phenomena of climate change, which denotes modifications to the full range of characteristics that characterize climate, is tied to global warming. Climate change affects not only changes in air temperature but also 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. Global Warming Effects, Impact of Global Warming, Impact of Global Warming | Global Warming Definition, Causes and Effects - 2022, Climatic Variation, Since the beginning of human civilization, there has been an "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.
To correctly define the terms global warming and climate change, it is first important to acknowledge that the Earth's climate has changed across a wide range of timescales, from a single human lifetime to billions of years. "Regimes" or "epochs" are commonly used to categorize this history of varied climatic conditions. For instance, there were significant changes in the global extent of glaciers and ice sheets throughout the Pleistocene glacial epoch (about 2,600,000 to 11,700 years ago). The distribution of solar energy throughout the Earth's surface changed over timeframes of tens to hundreds of millennia, which is what caused these variances.
The last glacial maximum, also known as the Last Glacial Maximum, occurred about 21,000 years ago and marked the end of the most recent ice age. At this time, continental ice sheets covered much of Europe and North America's central latitudes, extending as far south as modern-day London and New York City. It appears that the global annual mean temperature was 4-5 °C (7-9 °F) colder than it was in the middle of the 20th century. Keep in mind that these numbers represent an average for the entire world. In actuality, during the height of the last ice age, Earth's climate was characterized by greater cooling at higher latitudes (i.e., toward the poles) and relatively less cooling over much of the tropical oceans (near the Equator).
About 11,700 years ago, this glacial period abruptly came to an end, and the Holocene Epoch—a relatively ice-free age that followed—followed. According to standard definitions, the current era of Earth's history falls within the Holocene. However, other scientists have suggested that the Holocene Epoch ended in the relatively recent past and that the Earth is currently in a climate interval that is appropriately referred to as the Anthropocene Epoch, meaning that humans have had a significant impact on climate.
Significant variations in the global climate have occurred over the length of the Holocene, albeit less dramatically than the climate changes that took place during the Pleistocene Epoch. The atmospheric circulation and precipitation patterns during the early Holocene, around 9,000 years ago, appear to have been very different from those of today. For instance, there is proof that what is today the Sahara Desert once experienced quite moist circumstances. Only slight variations in the Holocene insolation pattern and their interactions with major climate events like the monsoons and the El Nio/Southern Oscillation were responsible for the transition from one climatic regime to another (ENSO).
Conditions throughout the middle Holocene, between 5,000 and 7,000 years ago, seem to have been relatively warm—possibly even warmer than they are now in some regions of the planet and during specific seasons. Because of this, this period is also known as the Mid-Holocene Climatic Optimum. However, it's not entirely obvious how warm the average near-surface air temperatures are right now. Higher altitudes in the Northern Hemisphere had warmer summers as a result of changes in the insolation pattern, but similar changes also brought about cooler winters in the Northern Hemisphere and year-round cool temperatures in the tropics. Thus, any changes in the mean temperature at the hemispheric or global scales were a balance of competing for seasonal and regional changes.
In comparison to middle Holocene levels, conditions appear to have cooled during succeeding millennia. The term "Neoglacial" has been used to describe this period. This cooling trend in the middle latitudes was accompanied by sporadic movements of mountain glaciers that were similar to (though much more modest than) the more significant movements of the major continental ice sheets during the Pleistocene climate epoch.
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 meter is 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 meter per year at the top of the Earth's atmosphere. Global Warming Effects, Impact of Global Warming, Impact of Global Warming | Global Warming Definition, Causes and Effects - 2022, Climatic Variation, The average annual surface insolation is 342 watts per square meter after accounting for the fact that only 50% of the planet's surface is exposed to solar radiation.
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. The same 70 units must be radiated back into space by the Earth's surface and atmosphere to maintain thermodynamic equilibrium in the absence of further problems. According to the Stefan-Boltzmann law, the amount of this emission of outgoing radiation is correlated with the temperature of the Earth's surface (and that of the lower layer of the atmosphere that is effectively in touch with the surface).
The greenhouse effect adds to the complexity of Earth's energy balance. The so-called greenhouse gases, primarily carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), are trace gases with certain chemical properties that absorb some of the infrared light emitted by the Earth's surface. A portion of the original 70 units does not directly escape to space as a result of this absorption. The net effect of absorption by greenhouse gases is to increase the total amount of radiation emitted downward toward Earth's surface and lower atmosphere because greenhouse gases emit the same amount of radiation that they absorb and because this radiation is emitted equally in all directions (that is, as much downward as upward).
Earth's surface and lower atmosphere must produce more radiation than the initial 70 units to maintain equilibrium. Therefore, a higher surface temperature is required. The end result is comparable, even if this method is not quite the same as that which controls a real greenhouse. In comparison to what would be anticipated in the absence of greenhouse gases, the presence of greenhouse gases in the atmosphere causes a warming of the surface and lower portion of the atmosphere (and cooling higher up in the atmosphere).
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