According to the report, global warming is “unequivocal,” and since the 1950s it’s “extremely likely” that human activities have been the primary cause, an effect known as anthropogenic global warming.
The report, which is the first of three major studies, presents the clearest picture yet of current climate science.
The report found that efforts to keep atmospheric warming below 2 degrees Celsius, or 3.6 Fahrenheit -- which many scientists say is the limit to avoid major disruption -- are not enough.
Analysis of geologic and climate records went back hundreds of thousands of years, and scientists say many of the changes observed since 1950 are "unprecedented over decades to millennia."
Since the Industrial Revolution, the burning of fossil fuels has been the primary force behind the observed 40 percent increase in atmospheric carbon dioxide concentrations.
"Greenhouse gases contributed a global mean surface warming likely to be in the range of 0.5°C to 1.3 °C over the period 1951−2010, with the contributions from other anthropogenic forcings, including the cooling effect of aerosols, likely to be in the range of −0.6°C to 0.1°C."
In other words, greenhouse gases can be connected to about 0.9°C of warming, offset by about 0.3°C cooling from human aerosol emissions, resulting in 0.6°C average global surface warming over the past 60 years.
Scientists also measured the effects of natural causes, including solar activity and ocean cycles.
"The contributions from natural forcings are likely to be in the range of −0.1°C to 0.1°C, and from internal variability likely to be in the range of −0.1°C to 0.1°C."
In other words, natural causes have had a negligible effect on global temperatures.
The panel predicts that global temperatures are likely to rise by 0.3 to 4.8°C (0.5-8.5°F) by the end of the century -- depending on how we control carbon emissions, and whether we implement geoengineering projects to reduce global temperatures.
The report warns that even if carbon emissions are stopped completely, the planet will continue warming for hundreds of years without geoengineering.
The report also predicts sea levels will rise faster, and Arctic ice will continue to melt at a high rate. Scientists are also "virtually certain" that the upper ocean has warmed from 1971 to 2010.
Climate skeptics are quick to point out the so-called "pause" in the increase in temperatures since 1998, but the IPCC report indicated El Nino effects could be responsible for the lull, though 15 years is too short a period to draw conclusions.