He says that the increased solar brightness over the past 20 years has not been enough to cause the observed climate changes, but believes that the impact of intense sunshine on the ozone layer and cloud cover could be affecting the climate more than the sunlight itself. (washingtontimes.com)
Model simulations of 20th century global warming typically use actual observed amounts of atmospheric carbon dioxide, together with other human (for example chloroflorocarbons or CFCs) and natural (solar brightness variations, volcanic eruptions,...) climate - forcing factors. (realclimate.org)
And it requires, as well, that Earth's climate be insensitive to well - measured increases in greenhouse gases at the same time that it is excessively sensitive to poorly known solar brightness changes. (polluterwatch.com)