What are the causes of Climate Change?

What are the causes of Climate Change?

The "greenhouse effect"⁶ — warming that happens as the atmosphere traps heat radiating from Earth into space — has been expanding due to human expansion since the mid-twentieth century, according to science.

The presence of such gases in the atmosphere inhibits heat from escaping. Long-lived gases that persist in the atmosphere semi-permanently and do not react physically or chemically to temperature changes are referred to as "forcing" climate change. "Feedbacks" are gases, such as water vapor, that respond physically or chemically to temperature changes.

The following gases contribute to the greenhouse effect:

^{Figure 3 Greenhouse gases molecules}

^{Figure 4 – Earth’s heat}

Human activities on Earth are altering the existing greenhouse. The combustion of fossil fuels such as coal and oil has increased the abundance of carbon dioxide in the atmosphere over the past century. This is because the combustion of coal or oil produces CO2 by combining carbon with oxygen. The clearance of land for agriculture, manufacturing, and other human activities has raised greenhouse gas emissions to a smaller degree.

Changes in the natural atmospheric greenhouse's outcomes are difficult to foresee, but the following results seem to be likely:

• Normally, the Earth's temperature would rise. Warmer temperatures can be welcomed in some areas, but not in others.
• Warmer weather could be likely result in more evaporation and more precipitation overall, but some particular regions could also see varying results. Indeed, some of them could becoming wetter and others dryer.
• A greater greenhouse effect would warm the ocean and cause glaciers and ice sheets to partly melt, increasing sea levels. When the ocean warms, the water expands, adding to the increase of sea level.
• Higher atmospheric carbon dioxide (CO2) levels may have both positive and negative impacts on crop yields outside of a greenhouse. Plant development can be aided by increased CO2 levels, according to some laboratory studies.

Droughts, flooding, and extreme temperatures are examples of climate extremes that can cause crop losses and endanger agricultural producers' livelihoods as well as community food security around the world.  Weeds, pests, and fungi could prosper in warmer temperatures, wetter winters and higher CO2 levels. Depending on the crop and ecosystem, climate will change likely exacerbate weeds and pests.

Finally, since increased CO2 stimulates plant growth, research has already shown that decreases the nutritional value of most crops by lowering protein and essential nutrient concentrations in most species of plants⁷.

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• PCC Fifth Assessment Report, 2014
• United States Global Change Research Program, "Global Climate Change Impacts in the United States," Cambridge University Press, 2009
• ^{Naomi Oreskes, "The Scientific Consensus on Climate Change," Science 3 December 2004: Vol. 306 no. 5702 p. 1686 DOI: 10.1126/science.1103618}

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Human Activity and Its Importance

In the past 150 years, the industrial processes that underpin our modern culture have increased atmospheric carbon dioxide levels from 280 parts per million to 414 parts per million.

The panel also argued that human-produced greenhouse gases like carbon dioxide, methane, and nitrous oxide are likely to be blamed for much of the observed rise in Earth's temperature over the past 50 years.

Irradiance of the Sun

Because the Sun is the essential source of energy that drives our climate system, it's appropriate to presume that changes in the Sun's energy output will cause the climate to change.

Solar variability has been shown to play a role in previous climate changes in experiments. For example, between around 1650 and 1850, a decrease in solar activity combined with an increase in volcanic activity is believed to have aided in the onset of the Little Ice Age, when Greenland cooled from 1410 to the 1720s and glaciers advanced in the Alps.

However, some lines of evidence show that current global warming is unrelated to changes in solar energy:

• The average amount of energy emitted by the Sun has remained constant or risen slightly since 1750.
• Warmer temperatures would be expected in all layers of the atmosphere if the warming was caused by a more active Sun. Instead, they've noticed a cooling in the upper atmosphere, as well as a warming at the surface and in the lower atmosphere because greenhouse gases trap heat in the lower atmosphere.
• Climate models that account for changes in solar irradiance are unable to replicate the observed temperature trend over the past century or more without accounting for an increase in greenhouse gas emissions.