There is a regular follower of this blog named John Swallow who is constantly asking me to provide him with a definitive proof of the notion that Anthropogenic (man-caused) Global Warming (AGW) is occurring and that it’s magnitude is sufficient for us to be concerned about. Well John, this post is being provided just for you! In it, I will answer your question as thoroughly as any question can be answered via the scientific method.
First, I must admit to you that I cannot do the impossible. By that I mean that for any complex system in nature no idea or theory can be “proven” beyond all levels of doubt to be absolutely correct. All we can do via science is test the theories at hand against experiments and then from those comparisons decide which of the candidate theories, if any, provide a good fit to the experiments. So John, for beginners, you first have to learn and accept this aspect of science if you want to remain within the domain of science. If you want more than that – you will have to look either to your crystal ball or a scientific quack.
Now let’s move on to consider what the field of science has learned about climate change so far. The specific science behind the “Greenhouse Effect” and CO2′s part in it goes back about 200 years (Fourier and then, Tyndall), and crude quantitative estimates of anthropogenic CO2’s role as a driver of future temperature increases goes back about 110 years (Arrhenius).
After many decades of tedious analysis since then on the part of scientists representing a variety of disciplines, and drawing results using many different parameters and venues to measure the intricacies of climate and AGW, science has come to a clear consensus: man is warming the biosphere. That is what the measurements and the best theory suggest. The onus then is upon those that are in disbelief of this theory to provide evidence to the contrary. And by “theory” here, I am referring to the rigorous scientific type; the kind of which supports things like gravity and evolution, for examples. I am not referring to philosophical iideas that cannot be tested by physical experiments.
Again, John, keep in mind, there are no absolute “proofs” in science, especially for relatively complex systems. There is just evidence – even when that evidence is overwhelming. In 2013, 10,885 peer reviewed studies were published regarding climate change and in only two was the notion of man-made global warming rejected. That is, only 0.01% of those papers provided what their authors considered to be evidence against AGW. Furthermore, the accuracy of those two studies is now even being questioned (see http://www.theguardian.com/environment/climate-consensus-97-per-cent/2014/nov/07/new-study-disputes-satellite-temperature-estimates). There are very few places in any areas of science where such a tiny amount of descent is present within its professional ranks. There is far more descent, for example, on Einstein’s theory of gravity. The basic ideas of Arrhenius concerning CO2’s effect on temperature have held up to the tests of time and in accordance with the scientific method his theory, only, has significant support today and is considered to provide the most likely explanation for the man-caused global warming being witnessed today.
So John, that’s how science works and guess what? The timing for answering your questions could not be better. It just happens that the largest and most comprehensive organization representing all of the research done all around the world in the vast area of climate change has just turned out its most up to date report. I am now referring to the 2014 Report of the IPCC. In accordance with the scientific method, you will find the most credible answers to your questions there and you can find that document at http://www.ipcc.ch/report/ar5/wg2/
I also realize that the full document might be too much for you (and most people) to digest. Therefore, I will also provide below a very abbreviated summary of the 2014 IPCC report which was provided by Mark Fischetti, a senior editor of Scientific American, and appeared in the Nov 3, 2014, issue of that journal. His summary included 29 points and reads as follows:
Concerning Climate changes:
- The atmosphere is getting hotter.
- The oceans are getting much hotter, and much more acidic.
- CO2 emissions are by far the largest cause of global warming and ocean acidification, and they are rising.
- Methane emissions are the second largest cause of warming, and they are rising.
- Since 1950 human activities have led to virtually all temperature rise.
- Natural forces have caused virtually none of the temperature rise.
- The largest human sources of CO2 emissions are burning fossil fuels, making cement and burning off gas (“flaring”) from oil and gas production.
- Sea level is rising, and at an increasing pace.
- Glaciers are melting, ice sheets are thinning, and Arctic sea ice is disappearing.
- Permafrost is thawing.
- In North America, snow pack is decreasing.
- The number of cold days and nights are decreasing.
- The number of hot days and nights are increasing.
- Heat waves will occur more often and last longer.
- Heavy rainstorms and snowstorms will become more intense and frequent.
- Overall, precipitation will rise in high latitudes and the equatorial Pacific. In mid-latitudes, dry areas will get drier, wet areas will get wetter.
- Species are vanishing at an alarming and ever-increasing rate.
- Most plants, small mammals and ocean organisms cannot adapt fast enough to keep up with changes.
- Global temperature rise greater than 2 degrees Celsius will compromise food supplies globally.
- Human health problems will get worse.
- Risks to poorer people are greater than for others, in all countries.
What to do:
- To avoid severe damage to natural and human systems, the world should keep global warming to less than 2 degrees C above pre-industrial levels.
- Without more mitigation than is being done today, the temperature is more likely than not to rise by 4 degrees C by 2100.
- Significant reductions in greenhouse gas emissions by 2050 can significantly reduce warming by 2100.
- Keeping greenhouse gases in the atmosphere below the equivalent of 450 parts per million of CO2 can keep warming below 2 degrees C.
- Levels are likely to stay below 450 ppm if human emissions are reduced 40 to 70 percent by 2050 compared with 2010 levels.
- Allowing levels to reach 530 ppm by 2100 gives the planet slightly better than 50-50 odds of staying below 2C; that would require reducing emissions 25 to 55 percent by 2050 versus 2010.
- To hit a target of 430 to 530 ppm by 2100, the world must invest several hundred billion dollars a year in low-carbon electricity sources and energy efficiency.
- It is highly unlikely the world will stay below 450 ppm without widespread use of carbon capture and storage technologies.
So there you have it, John, the very best answer to your questions that science can provide. If you still require a more definitive answer and, perhaps, one that is in concert with the state AGW denial that you appear to reside in, I’m afraid you’ll have to go outside the domain of science to get that – say perhaps to some corners of philosophy or religion. While I have considerable respect for both of those disciplines, this blog does not go there – it is merely about the science of AGW.