Human activities have significantly disturbed the natural carbon cycle by extracting longburied fossil fuels and burning them for energy, thus releasing CO2 to the atmosphere.

“Charney 1979 Climate Senstivity” is about 3oC for a doubling of CO2. The range shown is for climate sensitivities of 1.5 to 4.5.

(Global carbon emissions continued along a worst-case track during 2013. Note that estimated temperature increases are for this century only. For context, it took 12,000 years for the world to warm 5 degrees Celsius at the end of the last ice age. Image source: Global Carbon Project.) On the current track, global CO2 emissions will double in about 30 years. This pace of emissions increase is along the worst-case path projected by the UN’s IPCC. One that will hit 8.5 watts per meter squared of additional warming at the top of the Earth’s atmosphere and greater than 1,000 ppm CO2 equivalent greenhouse gas heat forcing by the end of this century. Such a massive increase from human sources does not include amplifying feedback emissions from global methane or CO2 stores such as those now apparently destabilizing in the Arctic. Such emissions could add an additional 20 to 30 percent or greater heat forcing on top of the human forcing, according to scientific estimates, by the end of this century. The massive blow would be more than enough to trigger a hothouse extinction event — one that could well rival or exceed the Permian (also known as ‘the great dying’) in its ferocity due to the very rapid pace of the human heat accumulation.

Global average temperature is one of the most-cited indicators of global climate change, and shows an increase of approximately 1.4°F since the early 20th Century. The global surface temperature is based on air temperature data over land and sea-surface temperatures observed from ships, buoys and satellites. There is a clear long-term global warming trend, while each individual year does not always show a temperature increase relative to the previous year, and some years show greater changes than others. These year-to-year fluctuations in temperature are due to natural processes, such as the effects of El Ninos, La Ninas, and the eruption of large volcanoes. Notably, the 20 warmest years have all occurred since 1981, and the 10 warmest have all occurred in the past 12 years.

No. Even if emissions of greenhouse gases were to suddenly stop, Earth’s surface temperature would not cool and return to the level in the pre-industrial era for thousands of years.

The present level of atmospheric CO2 concentration is almost certainly unprecedented in the past million years, during which time modern humans evolved and societies developed. The atmospheric CO2 concentration was however higher in Earth’s more distant past (many millions of years ago), at which time palaeoclimatic and geological data indicate that temperatures and sea levels were also higher than they are today.

No. Adding more CO2 to the atmosphere will cause surface temperatures to continue to increase. As the atmospheric concentrations of CO2 increase, the addition of extra CO2 becomes progressively less effective at trapping Earth’s energy, but surface temperature will still rise.

Climate Facts

Carbon Dioxide


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CO2 Concentrations Last 800,000 Years
The atmospheric concentration of CO2 is continuing to increase at about 3.2ppm/year, having surpassed 400ppm for several months in 2014.
CO2 is already in the atmosphere naturally, so why are emissions from human activity significant?
Human activities have significantly disturbed the natural carbon cycle by extracting longburied fossil fuels and burning them for energy, thus releasing CO2 to the atmosphere.
Global CO2 Emissions - Projected vs Actual (through 2014)
If we continue emitting CO2 at the current accelerating rate the result will very likely be a climate that is inhospitable to civilization as we know it
Is there a point at which adding more CO2 will not cause further warming?
No. Adding more CO2 to the atmosphere will cause surface temperatures to continue to increase. As the atmospheric concentrations of CO2 increase, the addition of extra CO2 becomes progressively less effective at trapping Earth’s energy, but surface temperature will still rise.