Global warming - which evidence do you believe?

Question

What specific evidence do you accept as causing global warming - or if you believe more than one factor is at work - what combination and why?

Answer 1

One irrefutable piece of evidence that can be demonstrated in any science lab is the ability of the 'greenhouse gases' to retain heat. That's undeniable and only a fool would attempt to do so. This is pure science. History, politics, religion, world events, Al Gore, the Sun etc have no bearing on this simple scientific fact.

If we increase levels of greenhouse gases there is only one possible outcome and that is that the atmopshere warms up (barring intervening or extraneous factors such as nuclear wars or asteroid strikes).

That's the simple science behind global warming, there's a whole load more complicated stuff as well that can be used to prove the theory of manmade GW.

For me, as a scientist and climatologist, it's the science that is definitive. There's 1001 things we can see for ourselves such as the retreating glaciers, but these are just indicators, they don't provide the absolute proof that the scientific method does.

Answer 2

I believe there is more than one factor at work. I believe the exact percentage each factor plays in global warming can only be estimated at this time, although they may be very good estimates. .

Here are some of the factors we know about:
1. CO2 emissions trapping the heat in our atmosphere.
2. Destruction and replacement of forests with roads, buildings, and cropland.
3. Absense of natural snow cover, that would, if present, help to reflect the suns rays and heat back into the atmosphere.
4. Natural fluctuations in earth's temperature that occur over thousands of years and have nothing to do with humans.

5. Denial of the evidence of global warming could also be considered as a factor, since it potentially delays the process of arriving at a reasonable solution to the problem.

Why this combination? I believe these to be factors in global warming because they are the cause and the effect. Obviously the climate of planet earth is more delicate and subject to change than we ever knew before or have yet experienced. In other words, if you CAUSE some basic surface features of earth that have existed for thousands of years (cooling forests and snow cover) to be removed, and replace them with not so cool roads and buildings and add and excessive amount of carbon dioxide, then you have the EFFECTS of global warming - disappearing glaciers and ice caps, rising sea levels, violent weather patterns, etc...

What is more interesting is the question of whether or not we can create a "green" economy and industry large enough to preserve the ideal conditions in climate that we humans have known for centuries and millenia? Since the theory and scientific fact is that we have contributed to global warming, it is only logical, reasonable to understand, and follows suit that we can also slow, reduce and ultimately stop our contribution to global warming and its effects.

Answer 3

While the man made global warming is based primarily on circumstantial evidence, there is evidence to suggest that solar activity is to blame for at least 35% of the warming observed up to 2000. And possibly much more if all of the positive feed back mechanisms are integrated into the analysis.


One of the last remaining mysteries that would solve the problem of how much of global warming is solar and how is caused by humanity, is the satellite record of solar energy levels reaching earth. Unfortunately there is not a consistent record over the last thirty years of total solar irradiance (TSI), so there are two basic TSI datasets, one called ACRIM and one called PMOD. Unfortunately the space shuttle challenger disaster caused a gap in the ACRIM data during a critical time of solar maximum, so there is some disagreement on how to bridge the gap.

http://www.acrim.com/

ACRIM by some climatologists put the warming in the last three decades at 35% solar or more.

PMOD puts the warming over the same period by only 10%.

See table 1 in the following paper for various trends computed.

http://www.fel.duke.edu/~scafetta/pdf/20...

If ACRIM were integrated into climate models and all of the positive feedback mechanisms associated with the increase in solar energy were properly factored in the solar based contribution to global warming would likely excede 35%, by a substantial margin.

Answer 4

I concur with earlier comments by Ken, JS & Dr. Blob. Your question has brought out attempts to deal with the question based on science from some of the other side, notably shapeshi, ecic, jim and tomcat. This is an encouraging sign. I think that the inclusion of the word believe in your question is the key. A better wording would be to accept the evidence rather than to believe. Belief has the connotation of accepting a dogma in the absence of direct evidence or proof.

Answer 5

Here's my summary of the evidence:

Basically we know it's warming, and we've measured how much:

http://www.ncdc.noaa.gov/img/climate/research/2005/ann/global-blended-temp-pg.gif

Scientists have a good idea how the Sun and the Earth's natural cycles and volcanoes and all those natural effects change the global climate, so they've gone back and checked to see if they could be responsible for the current global warming. What they found is:

Over the past 30 years, all solar effects on the global climate have been in the direction of (slight) cooling, not warming. This is during a very rapid period of global warming.

http://news.bbc.co.uk/2/hi/uk_news/6290228.stm
http://www.pubs.royalsoc.ac.uk/media/proceedings_a/rspa20071880.pdf

So the Sun certainly isn't a large factor in the current warming. They've also looked at natural cycles, and found that we should be in the middle of a cooling period right now.

"An often-cited 1980 study by Imbrie and Imbrie determined that 'Ignoring anthropogenic and other possible sources of variation acting at frequencies higher than one cycle per 19,000 years, this model predicts that the long-term cooling trend which began some 6,000 years ago will continue for the next 23,000 years.'"

http://en.wikipedia.org/wiki/Milankovich_cycle

So it's definitely not the Earth's natural cycles. They looked at volcanoes, and found that

a) volcanoes cause more global cooling than warming, because the particles they emit block sunlight

b) humans emit over 100 times more CO2 than volcanoes annually

http://www.gaspig.com/volcano.htm

So it's certainly not due to volcanoes. Then they looked at human greenhouse gas emissions. We know how much atmospheric CO2 concentrations have increased over the past 50 years:

http://en.wikipedia.org/wiki/Image:Mauna_Loa_Carbon_Dioxide.png

And we know from isotope ratios that this increase is due entirely to human emissions from burning fossil fuels. We know how much of a greenhouse effect these gases like carbon dioxide have, and the increase we've seen is enough to have caused almost all of the warming we've seen over the past 30 years (about 80-90%). You can see a model of the various factors over the past century here:

http://en.wikipedia.org/wiki/Image:Climate_Change_Attribution.png

This is enough evidence to convince almost all climate scientists that humans are the primary cause of the current global warming.

Answer 6

I believe the surface temperature record exaggerates the amount of warming because of microsite issues. The quality of these stations is being documented by photographs and ranked from CRN1 (excellent quality) to CRN 5 (very poor). Only 15% were CRN1 or CRN2.
http://surfacestations.org

Answer 7

For that guy that says that humans can't affect the world climate, hello!!! we live all around the world, where places like china and india house over 1 billion people alone respectively. To say that we can't affect the world is to say man doesn't exist.

Answer 8

There is an enormous amount of peer reviewed professional scientific literature on this topic.

One of the best sources is the IPCC (Intergovernmental Panel on Climate Change.

The IPCC reports are available at any good University library.

Answer 9

Here is some evidence on the skeptical side:

http://www.geocraft.com/WVFossils/Reference_Docs/The_Geologic_Record_and_Climate_Change.pdf

http://www.spacecenter.dk/research/sun-climate/Scientific%20work%20and%20publications/resolveuid/86c49eb9229b3a7478e8d12407643bed

http://icecap.us/images/uploads/Soon07-CO2-TempCORR-Preprint.pdf

http://www.space.com/scienceastronomy/060926_solar_activity.html

There is also some problems with the IPCC putting out flawed information to exaggerate the current warming period:

http://www.john-daly.com/hockey/hockey.htm

There are a lot of temperature monitoring stations that have artificial heat sources near by:

http://surfacestations.org/

Answer 10

There's so much evidence, from the melting of the ice in the Arctic and Antarctic to the growing deserts of the earth. But what I find most compelling are the charts showing average temperature rising in lockstep with increasing CO2 in the atmosphere since the beginning of the industrial age.