Temperatures on earth have increased approximately 1.8°F since the early 20th century.
Over this time period, atmospheric levels of greenhouse gases such as carbon dioxide (CO2) and methane (CH4) have notably increased.
The 2010 Anderegg study found that 97-98% of climate researchers publishing most actively in their field agree that human activity is primarily responsible for global climate change.
The study also found that the expertise of researchers unconvinced of human-caused climate change is "substantially below" that of researchers who agree that human activity is primarily responsible for climate change.
They contend that immediate international action to reduce greenhouse gas emissions is necessary to prevent dire climate changes.
The con side argues human-generated greenhouse gas emissions are too small to substantially change the earth’s climate and that the planet is capable of absorbing those increases.According to researchers at the Scripps Institution of Oceanography, up to 60% of the changes in river flow, winter air temperature, and snow pack in the western United States (1950-1999) were human-induced.A 2015 study found that global warming caused by human actions has increased extreme precipitation events by 18% across the globe, and that if temperatures continue to rise an increase of 40% can be expected.According to the US Geological Service, this disruption can include the "extinction of temperature sensitive aquatic species." , there is a "high degree of confidence" that the Texas and Oklahoma heat waves and drought of 2011, and heat waves and drought in Moscow in 2010, "were a consequence of global warming" and that "extreme anomalies" in weather are becoming more common as a direct consequence of human-caused climate change.Higher temperatures from global warming are also causing some mountainous areas to receive rain rather than snow.According to the National Snow and Ice Data Center, global warming from human-produced greenhouse gases is a primary cause of the "unprecedented" retreat of glaciers around the world since the early 20th century.According to a 2013 IPCC report, "glaciers have continued to shrink almost worldwide" over the prior two decades, and there is "high confidence" (about an 8 out of 10 chance) that Northern Hemisphere spring snow continues to decrease.According to a 2013 IPCC report there is "high confidence" (about an 8 out of 10 chance) that anthropogenic global warming is causing permafrost, a subsurface layer of frozen soil, to melt in high-latitude regions and in high-elevation regions.As permafrost melts it releases methane, a greenhouse gas that absorbs 84 times more heat than CO2 for the first 20 years it is in the atmosphere, creating even more global warming in a positive feedback loop.As sunlight hits the earth, some of the warmth is absorbed by greenhouse gases in the atmosphere such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (NO2).These gases trap heat and cause the planet to warm through a process called the greenhouse effect.