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This has led to increases in mean global temperature, or global warming. The likely range of human-induced surface-level air warming by 2010–2019 compared to levels in 1850–1900 is 0.8 °C to 1.3 °C, with a best estimate of 1.07 °C. This is close to the observed overall warming during that time of 0.9 °C to 1.2 °C.
The Intergovernmental Panel on Climate Change (IPCC) has organized many of the risks of climate change into five "reasons for concern." [1] [2] The reasons for concern show that these risks increase with increases in the Earth's global mean temperature (i.e., global warming).
This creates air pollution, including nitrous oxides and particulates, and is a significant contributor to global warming through emission of carbon dioxide, [275] for which transport is the fastest-growing emission sector. [276] By subsector, road transport is the largest contributor to global warming. [275]
From ancient times, people suspected that the climate of a region could change over the course of centuries. For example, Theophrastus, a pupil of Ancient Greek philosopher Aristotle in the 4th century BC, told how the draining of marshes had made a particular locality more susceptible to freezing, and speculated that lands became warmer when the clearing of forests exposed them to sunlight.
The controversies are, by now, mostly political rather than scientific: there is a scientific consensus that global warming is happening and is caused by human activity. [2] Public debates that also reflect scientific debate include estimates of how responsive the climate system might be to any given level of greenhouse gases (climate sensitivity).
Climate change can also be used more broadly to include changes to the climate that have happened throughout Earth's history. [32] Global warming—used as early as 1975 [33] —became the more popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Senate. [34] Since the 2000s, climate change has ...
World leaders are meeting in Paris this month in what amounts to a last-ditch effort to avert the worst ravages of climate change. Climatologists now say that the best case scenario — assuming immediate and dramatic emissions curbs — is that planetary surface temperatures will increase by at least 2 degrees Celsius in the coming decades.
This is done in the broader context of environmental history. This differs from paleoclimatology which encompasses climate change over the entire history of Earth. These historical impacts of climate change can improve human life and cause societies to flourish, or can be instrumental in civilization's societal collapse.