The report states that: some of the global warming since 1850 could be a recovery from the Little Ice Age rather than a direct result of human activities.
It is the “leading international body for the assessment of climate change,” * The first IPCC report (1990) contains the following graph of average global temperature changes over the past 1,000 years based upon proxies.
It shows a “Medieval warm period” that was warmer than the present era and a “Little Ice Age” that was cooler.
He informed the * In 2013, “Forecast the Facts”—a “grassroots human rights organization dedicated to ensuring that Americans hear the truth about climate change”—published the following graphic purporting to show a recent photo of the North Pole: * After publishing an article documenting the facts above, Just Facts contacted Forecast the Facts to offer an opportunity to respond. As of January 2016, Forecast the Facts has not replied or issued a correction.  * The natural variability of Earth’s climate is such that a glacier formerly existed on Hawaii, and glaciers once covered almost all of Canada, New England, and the northern central United States: * In addition to carbon dioxide emissions from the use of fossil fuels, other factors that have been implicated by scientists as primary causes of modern climate change include but are not limited to: * A central debate among scientists about man-made greenhouse gases involves how much natural processes reduce or amplify the effects of these gases.
Positive feedbacks amplify the effects, and negative feedbacks diminish them. * The climate models included in the 2007 IPCC report are programmed with positive feedbacks for water vapor that more than double the warming effect of CO2. This is based upon the fact that warmer air evaporates more water, thus creating more water vapor, which is a greenhouse gas.  states that the feedbacks used in climate models are based upon “methods that …
A caveat of this finding is that it is based upon weather balloon data, which “must be treated with great caution, particularly at [higher] altitudes….”  states that the “sign and the magnitude of the global mean cloud feedback depends on so many factors that it remains very uncertain.” This is because some types of clouds trap heat while others reflect it.   found that ice clouds (also called cirrus clouds) exert a “strongly negative” feedback to temperature changes, regardless of whether these changes are increases or decreases.
A caveat of this finding is that the feedback process operates “on a time scale of weeks,” and “it is not obvious whether similar behavior would occur on the longer time scales associated with global warming.”  * Other feedbacks that may have “a substantial impact on the magnitude, the pattern, or the timing of climate warming” include snow coverage, temperature gradients in Earth’s atmosphere, aerosols, trace gases, soil moisture changes, and ocean processes. * Per a 2003 report by the United Nations Food and Agriculture Organization, between the mid-1970s and late 1990s, apparent food consumption per person increased by 15% worldwide, 25% in developing countries, and more than 36% in China.* This graph is called the “hockey stick graph” because the curve looks like a hockey stick laid on its side (click on the footnote for a graphic illustration). The red part of the curve represents modern instrument-measured surface temperatures, the blue represents proxy data, the black line is a smoothed average of the proxy data, and the gray represents the margin of error with 95% confidence.  * This graph has been the subject of disputes in scientific journals,  congressional hearings,  and legal proceedings including a Freedom of Information Act lawsuit.  Just Facts presently does not have the resources to conclusively assess all the competing claims on this issue, but the facts we have verified are as follows: medieval warmth,” and shows the following graph of temperature changes for the Northern Hemisphere over the past 1,300 years.This graph, which is called a “spaghetti graph,” is constructed with data from 12 proxy studies spliced with instrument-measured surface temperatures (the dark black line): * The fifth IPCC report (2013) states that challenges persist in reconstructing temperatures before the time of the instrumental record “due to limitations of spatial sampling, uncertainties in individual proxy records and challenges associated with the statistical methods used to calibrate and integrate multi-proxy information.” This report contains the following spaghetti graphs of proxy studies spliced with instrument-measured surface temperatures (the black lines): * In 2009, an unknown individual(s) released more than 1,000 emails (many dealing with proxy studies) from the University of East Anglia’s Climatic Research Unit (CRU).Data from these instruments is used to calculate the average temperatures of different layers of the Earth’s atmosphere.  * The lowermost layer of the atmosphere, which is called the “lower troposphere,” ranges from ground level to about five miles (8 km) high.  According to satellite data correlated and adjusted by the National Space Science and Technology Center at the University of Alabama Huntsville, the average temperature of the lower troposphere increased by 0.60ºF (0.33ºC) between the 1980s and 2000s, mostly from 1997 to 2010: * Sources of uncertainty in satellite-derived temperatures involve variations in satellite orbits, variations in measuring instruments, and variations in the calculations used to translate raw data into temperatures.  * According to temperature measurements taken near the Earth’s surface that are correlated and adjusted by NASA’s Goddard Institute for Space Studies, the Earth’s average temperature warmed by 1.5ºF (0.8ºC) between the 1880s and 2000s, mostly during 1907–19–2014: * According to temperature measurements taken near the Earth’s surface that are correlated and adjusted by the Climatic Research Unit of the University of East Anglia in the U.K., the Earth’s average temperature warmed by 1.4ºF (0.8ºC) between the 1850s and 2000s, mostly during 1911-19-1998: * Sources of uncertainty in surface temperature data involve “very incomplete” temperature records in the earlier years, “systematic changes in measurement methods,” “calculation and reporting errors,”       data adjustments that are performed when instruments are moved to different locations, instrument precision, instrument positioning, and missing documentation/raw data.  definitive assessment of uncertainties is impossible, because it is always possible that some unknown error has contaminated the data, and no quantitative allowance can be made for such unknowns. * Oceans constitute about 71% of the Earth’s surface. Changes in air temperature over the world’s oceans are typically based on measurements of water temperature at depths varying from less than 3 feet to more than 49 feet.  This data is combined with changes in air temperature over land areas to produce global averages.  contrasted water and air temperature changes in the tropical Pacific Ocean using three sources of measurements.As of July 2015, no similar study has been conducted on a global basis. * From 1979–2014, the three temperate datasets posted above differed from one another by an annual average of 0.13ºF (0.07ºC).