Depending on which way your filter bubble is oriented, this will come out as pro GW or anti GW...
Everyone knows about the ice ages, but how many know about weather cycles that last decades or the ones that last centuries?
There is evidence of a warming/cooling cycle that lasts about 500 years. We are currently in a warming cycle that started about 1850. Before that we were in cooling cycle starting around 1300 (Little Ice Age). Before that was warming starting around 800 (Medieval Warm Period).
Briefly, during the Medieval Warm Period, marginal land became productive, british wine was of a quality it was cutting into the market for french wine, the Vikings established a colony in Greenland, and the Vikings found grapes growing in Newfoundland.
Soon after 1300, it got colder. Marginal land became unproductive again. The Vikings abandoned Greenland, The british wine industry tanked. And the glaciers in the european alps grew again. Eventually, since the Thames kept freezing solid enough, the british started having Frost Fairs on it. One show describing all this is 'Big Chill: The Little Ice Age' that is shown occasionally on Discovery/History/Science channel. This is history, not tree rings, satellite data, or arctic/antarctic ice cores.
I suggest all the weather observations of the past hundred years have been on the upslope of a natural warming cycle.
Not to say that humans aren't having an effect, with all the pollution we are pumping into the atmosphere. Another show I saw was Nova: Dimming the Sun. In it they talked about some measurable effects of human pollution.
In this show they studied how much solar radiation reached the ground before /after and during the air industry shutdown after 9/11. They studied the atmosphere and how much solar radiation is reaching the ground when there were no jet contrails crisscrossing the sky. The also studied a thousand mile island chain off of India. In comparing the north and south ends of this chain they saw the northern end, typically covered by pollution from India, received much less sunlight than the southern end of the chain which is pristine. They discussed the difference between clouds made of water droplets condensed around natural particles versus manmade particles. The ones from manmade particles reflect ten time more sunlight than clouds made from water droplets formed around natural particles.
You may have heard one of the schemes to cool the earth is to inject sulfur particles into the upper atmosphere to form more reflective clouds. I remember in the 70s and 80s when there was a big push to clean up the smoke stacks and get the lead out of gasoline because of acid rain and fears of global cooling. The recent scheme of injecting sulfur into the atmosphere made me think we could just take the pollution filters off the smokestacks and accomplish the same things. Either way, we will have acid rain again.
While I am for being ‘greener’, I don't think we know enough about climate change and what is feeding into it to make wise decisions about geoengineering our planet. And before one of you throws in an 'occams razor' comment, I must point out that razor only works if you have sufficient information and sufficient understanding of that information to draw a reasonable conclusion.
We don't know all of what is feeding into the climate, from solar output, to pollution, to volcanoes, to the recent discovery that the mid-ocean ridges are more volcanically active that previously thought.(http://science.slashdot.org/story/16/01/12/222234/the-40000-mile-volcano?utm_source=rss1.0mainlinkanon&utm_medium=feed). While I think we can reasonably do more to pollute less, I think we should do a lot more to help Brazil, China, and India curb their pollution (which far outweighs ours).