How much global warming is caused by humans

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The figure below shows the estimated role of each different climate forcing in changing global surface temperatures since records began in — including greenhouse gases red line , aerosols dark blue , land use light blue , ozone pink , solar yellow and volcanoes orange.

The black dots show observed temperatures from the Berkeley Earth surface temperature project, while the grey line shows the estimated warming from the combination of all the different types of forcings. The combination of all radiative forcings generally matches longer-term changes in observed temperatures quite well.

There are also periods from and where some larger disagreements are evident between projected and observed warming, both in this simple model and in more complex climate models. The chart highlights that, of all the radiative forcings analysed, only increases in greenhouse gas emissions produce the magnitude of warming experienced over the past years.

If greenhouse gas emissions alone were warming the planet, we would expect to see about a third more warming than has actually occurred. The extra warming from greenhouse gases is being offset by sulphur dioxide and other products of fossil fuel combustion that form atmospheric aerosols. Aerosols in the atmosphere both reflect incoming solar radiation back into space and increase the formation of high, reflective clouds, cooling the Earth.

Ozone is a short-lived greenhouse gas that traps outgoing heat and warms the Earth. Ozone is not emitted directly, but is formed when methane, carbon monoxide, nitrogen oxides and volatile organic compounds break down in the atmosphere. Increases in ozone are directly attributable to human emissions of these gases.

In the upper atmosphere, reductions in ozone associated with chlorofluorocarbons CFCs and other halocarbons depleting the ozone layer have had a modest cooling effect. The net effects of combined lower and upper atmospheric ozone changes have modestly warmed the Earth by a few tenths of a degree. For example, replacing a forest with a field will generally increase the amount of sunlight reflected back into space, particularly in snowy regions.

The net climate effect of land-use changes since is a modest cooling. Volcanoes have a short-term cooling effect on the climate due to their injection of sulphate aerosols high into the stratosphere, where they can remain aloft for a few years, reflecting incoming sunlight back into space.

However, once the sulphates drift back down to the surface, the cooling effect of volcanoes goes away. The orange line shows the estimated impact of volcanoes on the climate, with large downward spikes in temperatures of up to 0. Finally, solar activity is measured by satellites over the past few decades and estimated based on sunspot counts in the more distant past. The amount of energy reaching the Earth from the sun fluctuates modestly on a cycle of around 11 years. There has been a slight increase in overall solar activity since the s, but the amount of additional solar energy reaching the Earth is small compared to other radiative forcings examined.

Over the past 50 years, solar energy reaching the Earth has actually declined slightly , while temperatures have increased dramatically.

The accuracy of this model depends on the accuracy of the radiative forcing estimates. Some types of radiative forcing like that from atmospheric CO2 concentrations can be directly measured and have relatively small uncertainties. Others, such as aerosols, are subject to much greater uncertainties due to the difficulty of accurately measuring their effects on cloud formation.

These are accounted for in the figure below, which shows combined natural forcings blue line and human forcings red line and the uncertainties that the statistical model associates with each. These shaded areas are based on different estimates of radiative forcings, incorporating research attempting to estimate a range of values for each.

Uncertainties in human factors increase after , driven largely by increases in aerosol emissions after that point. Global mean surface temperatures from Berkeley Earth black dots and modelled influence of all combined natural blue line and human red line radiative forcings with their respective uncertainties shaded areas for the period from to But Venus has about , times as much carbon dioxide in its atmosphere as Earth and about 19, times as much as Mars does , producing a runaway greenhouse effect and a surface temperature hot enough to melt lead.

The above graph compares global surface temperature changes red line and the Sun's energy that Earth receives yellow line in watts units of energy per square meter since Eleven-year averages are used to reduce the year-to-year natural noise in the data, making the underlying trends more obvious.

Over the same period, global temperature has risen markedly. It is therefore extremely unlikely that the Sun has caused the observed global temperature warming trend over the past half-century. Images of Change. Explore a stunning gallery of before-and-after images of Earth from land and space that reveal our home planet in a state of flux. Climate Mobile Apps. Keep track of Earth's vital signs, see the planet in a state of flux and slow the pace of global warming with NASA's free mobile apps.

Climate Time Machine.