How much of the apparent increase in global temperatures can be attributed to human activities?

Question

Please cite sources to back your answer.

Answer 1

Well you can attribute all of it it if to invisible pink unicorns if you like you like. The question isn't how much of it can be attributed to humans activities, the question is how much can REASONABLY be attributed to human activities.

And the answer is that we can't reasonably attribute most of it to human activities.

In science we set a 95% confidence limit on results in order for them to be accepted. What that means is that we have to be 95% certain that something couldn't result from random chance and natural events before we acknowledge that it is real. We set that 95% limit because the real world is complicated and sometimes things look like they are cause and effect when in fact they are coincidence.

The world's climate changes constantly, it always has. The question is whether the current warming is due to human activities, or whether it is a natural event that coincidentally happened to start just after industrialisation.

So what is the truth? Well the world's peak body on this issue, the IPCC states that it is impossible to separate out human (anthropogenic) and natural effects in this issue.

"Key Uncertainties: Magnitude and character of natural climate variability. Climate forcings due to natural factors and anthropogenic aerosols (particularly indirect effects)"

"most of the observed warming over the last 50 years is likely [66% to 90% chance] to have been due to the increase in greenhouse gas concentrations"

And that is it. We can only be 60-90% confident that a majority of what we see is human induced. We are not able to reach that 95% confidence level that this event is real.

From a scientific viewpoint we simply don't have the evidence to conclude that the majority of the current warming is due to human activities. Some of it certainly is, but as far as we can tell scientifically the majority of it is natural.

And as for what the latest science tells us:

“results suggest that 20th Century warming trends are plausibly a continuation of past climate patterns. Results are not precise enough to solve the attribution problem by partitioning warming into natural versus human-induced components. However, anywhere from a major portion to all of the warming of the 20th Century could plausibly result from natural causes according to these results.”

Loehle, C. 2004; “Climate change: detection and attribution of trends from long-term geologic data.” Ecological ModeModeModelling

Answer 2

To answer your question, a lot, but it's impossible to know for sure. What we do know for sure is humans are a significant cause.

CO2 is 30% higher than it has been for 650,000 years. Methane is 130% greater. These are two of the main pollutants humans put into the atmosphere in excess, and they are two of the primary greenhouse gases.

Look at the 'hockeystick', which shows a dramatic warming since 1950 after a fairly stable climate for 1000 years. In fact, the 10 hottest years in recorded history have all happened since 1990, with 2005 being the hottest, and 2006 is shaping up to maybe break that record.
(see links below)

How's that for proof of man's fault in this? There is ample proof, any real scientist will tell you that.

There has NEVER been an article doubting man's influence on global warming published in a peer-reviewed journal. A recent study of almost 1000 proved that.

Yes, the earth naturally heats and cools, but the rate and amount we are warming now is unprecedented in the recent geologic past. We are doing this, and we must stop it. This is not some political statement or rhetoric. This is science trying to educate a crass, ignorant public of the damage they are doing. The magnitude of temperature increase ALREADY is about 10x that of the 'little ice age' of the middle ages, and rate and amount are only going up.

Just to be clear, glacial and interglacial cycles are mainly controlled by astronomical fluctuations, but we have a detailed record of the last 7 cycles, and what the climate and CO2 is doing now is way different and extreme. The rate of increase is much higher than in the past AND the value itself is much higher.

HI CO2:
http://news.bbc.co.uk/1/hi/sci/tech/4467420.stm
HOCKEY STICK:
http://news.bbc.co.uk/1/hi/sci/tech/5109188.stm
General climate stuff:
http://news.bbc.co.uk/1/hi/sci/tech/3897061.stm

Answer 3

The environmentalist say that CO2 has increased 30% and that intensifies the solar heat. WRONG Measure it the amount of CO2 is 1 to 2 parts per million,that is nothing,but look at all the CO2 that man is producing,where did it go????? Find out and u will have the answer. If there isn't the CO2 to intensify the heat then there is no global warming. What is doing it is our green plants that take in CO2 and put out oxygen.

Answer 4

it would say about 92 percent, though some might be indirectly , this is due to the fact of human evolution and development, such as industrialization and development of various products

Answer 5

most!!!