There is ample evidence that climate change is happening. 97% of scientists believe not only that climate change is happening, but that humans are causing climate change.

The National Climate Assessment is a report compiled by over 300 experts guided by the Federal Advisory Committee. Below are some of the key facts that that report uses to demonstrate climate change’s existence:

Global Temperatures are Rising

One of the key aspects of climate change is global warming. While this might not feel like the case during especially cold days of winter, it is unequivocally true. The last three years: 2017, 2016, and 2015 have been the three hottest years on record.  The organization Climate Central also points out that “The five warmest years in the global record have all come in the 2010s. The 10 warmest years on record have all come since 1998, [and] The 20 warmest years on record have all come since 1995.”

Looking beyond the last 20 years, the National Climate Assessment shows that in each successive decade since 1930, the average global temperature has increased. The 1980s were the warmest decade on record, surpassed by the 1990s, surpassed by the 2000s.

 

Temperature Rise

As a result of this warming, and to further demonstrate its existence, the National Climate Assessment points out that the following is also true:

  • Snow and ice cover has decreased in most areas with the most drastic reductions at the poles. In fact, minimum arctic sea ice (usually during September) has decreased by more than 40%. NCA states that “This decline is unprecedented in the historical record, and the reduction of ice volume and thickness is even greater.”
  • Sea level is increasing because as water warms it expands and melting ice and icecaps adds water to the oceans.
  • Atmospheric water vapor is increasing because warmer air can hold more water.

Extreme heatwaves and heavy precipitation events (storms, hurricanes, etc.) have become more frequent.

Increases in Greenhouse Gasses Are Driving This Increase in Temperature

The cause of this warming is also unequivocal. As the concentration of C02 increases in the atmosphere, the global temperature increases.

 

Temp and CO2

 

Note: The NCA states that “Red bars show temperatures above the long-term average, and blue bars indicate temperatures below the long-term average. The black line shows atmospheric carbon dioxide (CO2) concentration in parts per million (ppm). While there is a clear long-term global warming trend, some years do not 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 Niños, La Niñas, and volcanic eruptions. (Figure source: updated from Karl et al. 2009).”

While it is true that the climate has changed in the past due to natural factors, natural factors alone cannot explain the speed of temperature increase and global changes that we are experiencing now. In fact, research indicated that if we only looked at natural factors, the earth should be entering a global cooling stage. However, there is ample evidence that the opposite is true.

NCA explains that, “Since the beginning of the Industrial Revolution, humans have been increasingly affecting global climate, to the point where we are now the primary cause of recent and projected future change. The majority of the warming at the global scale over the past 50 years can only be explained by the effects of human influences, especially the emissions from burning fossil fuels (coal, oil, and natural gas) and from deforestation.”