The Role of Human Activity (in Global Warming)

Carbon Dioxide And Global Warming – How Do We Know?

Online. —  NASA has an easy-to-read summary of the Global Warming situation online at:

So, before it could be cancelled, for any reason, it seems wise to keep most of it intact and highlight some of the key statements it makes.

One of these is about man’s influence at To Quote:

In its Fifth Assessment Report, the Intergovernmental Panel on Climate Change, a group of 1,300 independent scientific experts from countries all over the world under the auspices of the United Nations, concluded there’s a more than 95 percent probability that human activities over the past 50 years have warmed our planet.

The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels from 280 parts per million to 400 parts per million in the last 150 years.

The panel also concluded there’s a better than 95 percent probability that human-produced greenhouse gases such as carbon dioxide, methane and nitrous oxide have caused much of the observed increase in Earth’s temperatures over the past 50 years.

The panel’s full Summary for Policymakers report is online at

Solar irradiance

It’s reasonable to assume that changes in the sun’s energy output would cause the climate to change, since the sun is the fundamental source of energy that drives our climate system.

Indeed, studies show that solar variability has played a role in past climate changes. For example, a decrease in solar activity is thought to have triggered the Little Ice Age between approximately 1650 and 1850, when Greenland was largely cut off by ice from 1410 to the 1720s and glaciers advanced in the Alps.

But several lines of evidence show that current global warming cannot be explained by changes in energy from the sun:

Since 1750, the average amount of energy coming from the sun either remained constant or increased slightly.

If the warming were caused by a more active sun, then scientists would expect to see warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere, and a warming at the surface and in the lower parts of the atmosphere. That’s because greenhouse gases are trapping heat in the lower atmosphere.

Climate models that include solar irradiance changes can’t reproduce the observed temperature trend over the past century or more without including a rise in greenhouse gases.


IPCC Fifth Assessment Report, 2014

United States Global Change Research Program, Global Climate Change Impacts in the United States,” Cambridge University Press, 2009

Naomi Oreskes, “The Scientific Consensus on Climate Change,” Science 3 December 2004: Vol. 306 no. 5702 p. 1686 DOI: 10.1126/science.1103618

Mike Lockwood, “Solar Change and Climate: an update in the light of the current exceptional solar minimum,” Proceedings of the Royal Society A, 2 December 2009, doi 10.1098/rspa.2009.0519;

Judith Lean, “Cycles and trends in solar irradiance and climate,” Wiley Interdisciplinary Reviews: Climate Change, vol. 1, January/February 2010, 111-122.

We don’t believe it could be stated any more clearly than that!