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Two millennia of mean surface temperatures according to different reconstructions from climate proxieseach smoothed on a decadal scale, with the instrumental temperature record overlaid in black. Multiple independently produced datasets confirm that from to the global average land and ocean free global warming pdf file temperature increased by 0.
The rest has melted ice and warmed the continents and the atmosphere. Regional effects of global warming and Cold blob North Atlantic Difference between average temperature in — compared to the period, showing strong arctic amplification.
Global warming refers to global averages. It is not uniform around the world: Although more greenhouse gases are emitted in free global warming pdf file Northern than in the Southern Hemisphere, this does not contribute to the difference in warming because the major greenhouse gases persist long enough to diffuse within and between the two hemispheres.
One climate commitment study concluded that if greenhouse gases were stabilized at year levels, surface temperatures would still increase by about 0. Some of this surface warming would be driven by past natural forcings which have not yet reached equilibrium in the climate system.
Some climatologists have criticized the attention that the popular press gives to "warmest year" statistics. Attribution of recent climate change By itself, the climate system may generate random changes in global temperatures for years free global warming pdf file decades at a time, but long-term changes emanate only from so-called external forcings.
Global warming - Wikipedia
Greenhouse gasGreenhouse effectRadiative forcingCarbon dioxide in Earth's atmosphereand Earth's energy budget The greenhouse effect is the process by which absorption and emission of infrared radiation by gases in a planet's atmosphere warm its lower atmosphere and surface.
It was proposed by Joseph Fourier indiscovered in by John Tyndall was first investigated quantitatively by Svante Arrhenius in and the hypothesis was reported in the popular press free global warming pdf file early as The rest of this increase is caused mostly by changes in land-use, particularly deforestation.
According to professor Free global warming pdf file Hoskinsthis is likely the first time CO2 levels have been this high for about 4. Attributions of emissions due to land-use change are subject to considerable uncertainty.
Atmospheric particles from these and other sources free global warming pdf file have a large effect on climate through the aerosol indirect effect.
Global dimminga gradual reduction in the amount of global direct irradiance at the Earth's surface, was observed from until at least They exert a cooling effect by increasing the reflection of incoming sunlight.
Removal by clouds and precipitation gives tropospheric aerosols an atmospheric lifetime of only about a week, while stratospheric aerosols can remain for a few years. Carbon dioxide has a lifetime of a century or more, and as such, changes in aerosols will only free global warming pdf file climate changes due to carbon dioxide.
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, a phenomenon known as the Twomey effect. Indirect effects of aerosols represent the largest uncertainty in radiative forcing. Atmospheric soot directly absorbs solar radiation, which heats the atmosphere and cools the surface.
Contribution of natural factors free global warming pdf file human activities to radiative forcing of climate change.
This changes climate by changing the seasonal and latitudinal distribution of free global warming pdf file solar energy at Earth's surface.
Climate change feedbackClimate sensitivityand Arctic amplification The dark ocean surface reflects only 6 percent of incoming solar radiation, whereas sea ice reflects 50 to 70 percent.
Positive feedbacks increase the response of the climate system to an initial forcing, while negative feedbacks reduce it.