External forcings include natural phenomena such as volcanic eruptions and variations in the sun's output. Radiative forcing is a measure of how various factors alter the energy balance of the Earth's atmosphere. Between the start of the Industrial Revolution inand the yearthe increase in the atmospheric concentration of carbon dioxide chemical formula: CO2 led to a positive radiative forcing, averaged over the Earth's surface areaof about 1.
Weather station records and ship-based observations indicate that global mean surface air temperature warmed between about 0.
Although the magnitude of warming varies locally, the warming trend is spatially widespread and is consistent with an array of other evidence detailed in this report.
The ocean, which represents the largest reservoir of heat in the climate system, has warmed by about 0. The observed warming has not proceeded at a uniform rate.
Virtually all the 20th century warming in global surface air temperature occurred between the early s and the s and during the past few decades. The causes of these irregularities and the disparities in the timing are not completely understood.
Are greenhouse gases causing climate change? The stated degree of confidence in the IPCC assessment is higher today than it was 10, or even 5 years ago, but uncertainty remains because of 1 the level of natural variability inherent in the climate system on time scales of decades to centuries, 2 the questionable ability of models to accurately simulate natural variability on those long time scales, and 3 the degree of confidence that can be placed on reconstructions of global mean temperature over the past millennium based on proxy evidence.
Despite the uncertainties, there is general agreement that the observed warming is real and particularly strong within the past 20 years. Whether it is consistent with the change that would be expected in response to human activities is dependent upon what assumptions one makes about the time history of atmospheric concentrations of the various forcing agents, particularly aerosols.
By how much will temperatures change over the next years and where? Climate change simulations for the period of to based on the IPCC emissions scenarios yield a globally-averaged surface temperature increase by the end of the century of 1.
The wide range of uncertainty in these estimates reflects both the different assumptions about future concentrations of greenhouse gases and aerosols in the various scenarios considered by the IPCC and the differing climate sensitivities of the various climate models used in the simulations.
The range of climate sensitivities implied by these predictions is generally consistent with previously reported values.
The predicted warming is larger over higher latitudes than over low latitudes, especially during winter and spring, and larger over land than over sea. Rainfall rates and the frequency of heavy precipitation events are predicted to increase, particularly over the higher latitudes.
Higher evaporation rates would accelerate the drying of soils following rain events, resulting in lower relative humidities and higher daytime temperatures, especially during the warm season.
The likelihood that this effect could prove important is greatest in semi-arid regions, such as the U.
These predictions in the IPCC report are consistent with current understanding of the processes that control local climate. In addition to the IPCC scenarios for future increases in greenhouse gas concentrations, the committee considered a scenario based on an energy policy designed to keep climate change moderate in the next 50 years.
This scenario takes into account not only the growth of carbon emissions, but also the changing concentrations of other greenhouse gases and aerosols.
Sufficient time has elapsed now to enable comparisons between observed trends in the concentrations of carbon dioxide and other greenhouse gases with the trends predicted Page 4 Share Cite Suggested Citation: An Analysis of Some Key Questions.
The National Academies Press. The increase of global fossil fuel carbon dioxide emissions in the past decade has averaged 0. It is not known whether these slowdowns in growth rate will persist.
How much of the expected climate change is the consequence of climate feedback processes e.Joe Fone begins by revealing the historical roots of the "human-caused global warming" hypothesis. He then goes into a exhaustive and detailed discussion of the underlying science, showing its many inconsistencies with current facts and figures.
A polar flyover with NASAs IceBridge mission reveals the ravages of climate change on Antarctica. Oct 20, · Dozens of pages of resources, meant to help local governments deal with climate change, have been removed or revised from an agency site, according to a monitoring group.
Climate change is a change in the statistical distribution of weather patterns when that change lasts for an extended period of time (i.e., decades to millions of years). Climate change may refer to a change in average weather conditions, or in the time variation of weather within .
Even as President Donald Trump downplays the importance of climate change, there are signs that Americans may be taking it more seriously—at least when it comes to buying a house. Jesse Keenan, who teaches at Harvard University and focuses on the interaction between climate change and the housing market, said that connection is increasing as more Americans live through storms, floods or wildfires.
Jesse Keenan, who teaches at Harvard University and focuses on the interaction between climate change and the housing market, said that connection is increasing as more Americans live through storms, floods or wildfires. Read chapter Summary: Climate Change Science: An Analysis of Some Key Questions Login Register Cart Help. Climate Change Science: An Analysis of Some Key Questions () How much of the expected climate change is the consequence of climate feedback processes (e.g., water vapor, clouds, snow packs)? Global demand for livestock products is expected to double by , mainly due to improvement in the worldwide standard of living. Meanwhile, climate change is a threat to livestock production because of the impact on quality of feed crop and forage, water availability, animal and milk production, livestock diseases, animal reproduction, and biodiversity.