For example, 100 million years ago there was ten times the CO2 in the air that there is today. There were no mass extinctions associated with that concentration. Mammals were roaming the surface then and the planet didn't die in a ball of flame.
There is no overwhelming consensus in the scientific community regarding the degree to which humans are impacting climate. If you listen to the IPCC you would think there is no debate and the Earth is doomed. The IPCC, however, hand picks scientific studies to support their view and even directly funds studies. The IPCC is a group of bureaucrats and politicians, with few scientists guiding their agenda.
There are groups of climate scientists that disagree with the IPCC's contentions.
The atmosphere appears to be warming in the Northern Hemisphere, but not so much in the Southern Hemisphere.
Personally I hope global warming is real and it's okay with me that humans are playing a role. The reason is because Earth is due to return to an ice age and global warming may postpone that event. Also, people seem to forget, that CO2 is the main food for plants. The addition of CO2 is actually fertilizing the living Earth. Global warming will also extend growing seasons and the extent of arable land.
Earth's climate is changing and has always changed. If you look at the fossil record, you see long periods (talking geologic time scales) where particular regions remained fairly constant and you see where local climates which changed gradually over long times and you see fairly rapid changes in climate and you even see "almost instant" climate change across vast regions due to volcanic eruptions and meteor impacts and, maybe, due to things we have not identified yet.
So... the fossil record is completely "natural" because modern humans do not show up in it until basically the very last fraction of the last letter in the last word in the final credits of the film.
All that said... There is a LOT of data that shows very clearly that, at least in the very recent geologic past, say couple hundred thousand years, we are experiencing wild spikes in measurements such as ocean temperature and CO2 concentration and melting of glaciers and distribution of heavy rainfall and drought and temperature extremes (highs and lows) and ocean acidity and on and on. And... these spikes have gotten much more wild in the past 300 years (since human activity has been growing exponentially). Coincidence??? Could be.
But... If human activity is contributing to making these spikes worse and if you appreciate living in human society as it is right now, where most of us know that our next meal is available at any grocery store or restaurant and that we don't worry about freezing to death or dying of thirst or drowning or dying of diseases that are spread by parasites, then you might want to pay attention to what humans are doing and you might consider taking some steps to decrease the human contribution.
Both. Humans can affect the environment and nature can as well. The current long term trend of warming, however, is chiefly due to humans.
What happens when we increase the amount of CO2 in the atmosphere? To find out we look at a University level text book written by David Archer, a professor at the Department of The Geophysical Sciences at the University of Chicago. If you scroll down to figure 4-5 near the bottom of the following page we can see that, while the middle of the CO2 absorption band remains relatively static after a certain concentration is reached, the band does not get deeper but gets wider with increasing CO2 concentration.
http://forecast.uchicago.edu/archer.ch4....
Next we look at the changes in tropospheric radiation. Griggs published a paper in 2007 that did just that. If we look at the various graphs on the paper in the following link we see a range of measured frequencies from 700cm^-1, the right hand side of the CO2 absorption band and the point where we will see the most change if the increase is due to CO2, and 1200cm^-1. And, in fact, between the years 1970 and 2003, the study period, we see just that.
http://journals.ametsoc.org/doi/pdf/10.1...
This study is an extension of a study by Harries in 2001.
https://workspace.imperial.ac.uk/physics...
Now that we know the warming is due to increases in CO2 we need to find out where that additional CO2 is coming from. Historically during warming periods CO2 concentration has risen after temperatures increase due to what is known as Le Chatelier's Principal, which states if a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change and a new equilibrium is established. However, as we are currently using fossil fuels from what is known as the geological carbon cycle and pumping them back into what is known as the biological carbon cycle we are throwing that natural balance off. The result being an increase in the partial pressure, or weight, of that CO2 above the surface of the ocean and the oceans trying to maintain equilibrium. They are actually absorbing more CO2 than they are emitting during a warming period, as evidenced by their decreasing pH or acidification, which would not occur naturally.
http://www.bu-eh.org/uploads/Main/doney_...
For more proof we can look at measurements of increasing atmospheric CO2, which is currently rising at an average rate of 2 parts per million (ppm) or 15.6 billion tonnes annually, and estimates of human emissions, which stands at over 33.5 billion tonnes annually.
http://www.esrl.noaa.gov/gmd/ccgg/trends...
http://cdiac.ornl.gov/ftp/ndp030/global....
The vast majority of climate scientists believe that it is primarily the result of human activity. Being an Emeritus scientist (but not a climate scientist), I will side with science every time. To do otherwise is to descend into political/religious dogma.
The best way to get a Grant from the government is to imply there is a problem. Now to get more dollars your results better verify there is a problem.
In a bad economic climate many are living on government Grants.
Natural. Global Warming was on for 34 years and now that its over Nature is slowly trying to return all climates back to normal everywhere,. so be patient. Mike
Both
