How much of the observed global warming is caused by humans? How much warmer is it than its supposed to be?

Question

What is the actual measured impact of humans on the climate?

Answer 1

The earth is NOT any warmer now than it is supposed to be. In fact, the earth is now COOLER than what could be considered normal. The earth is currently in an interglacial period of an ICE AGE. The earth has been in an ice age for the last 40 million years. Over the earth's total history, it has been in an ice only approx. 15% of the time. Thus, the current ice age means that the earth is colder than normal.

As far as how much of global warming is caused by humans, the answer is very little. The earth has seen a relatively minor period of warming of the last century following several centuries of cooling known as the 'little ice age.' The little ice age was caused by a reduction in the sun's output known as the maunder minimum. As the sun's output has increased again, the earth's temperature has increased accordingly. Studies of the number of sunspots show an almost exact correlation between the 11 year sunspot average over the last century and the temperature rise on earth. However, the number of sunspots is not the only cause of warming. The size of sunspots and size and intensity of the magnetic plage areas around the sunspots also affect the earth's temperature. As comprehensive study of these phenomenon show that the increase in solar irradiation over the last century account for 80% of the earth's warming over that time.

Answer 2

Global Warming is an issue, but not one we need to address, the earth has cycles- when the dinosaurs roamed the earth the actual temperature was much warmer, then the earth froze, and it goes thru this cycle with or with out us. The human impact is known to cause some warming but the earth will take care of us just as it did the dinosaurs- we will be gone soon enough, so dont worry about global warming- the earths center is so hot the the earth will naturally warm it self over time, and there is nothing we can do about it.

Answer 3

Short Answer
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How much is caused by humans - between 78 and 98%

How much warmer - between 0.7 and 1.2°C


Explanation
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No-one can give you a definite answer and that's because we can't say for sure what role nature is playing in the current warming trend, we have a good idea but can't be specific.

We can accurately reconstruct natural behaviour for the last 800,000 years and can work out to within an accuracy of about 0.1°C what the temperature has been over this time.

We know from this data there are warming and cooling trends, sometimes lasting a few years and sometimes lasting for thousands of years. In many cases we know what caused them, but not always.

Analysis of the data provides parameters within which nature operates. Knowing these limits enables us to fix maximum and minimum values to the natural contribution.

Depending just how we do this determines the result we get. If we look at the temperature record as a whole for the 10,000 years prior to industrialisation we see that globally the average tempertaures rose by 1°C. If we continue this trend for the 200 years to date we could conclude that naturally the planet should have warmed by 0.02°C.

However, we could also look at the period of the last glacial retreat when temperatures were much faster - nearly 0.001°C per year. On this basis the natural rise in temps in the last 200 years could have been as much as 0.2°C.

So, nature could have caused temp rises of between 0.02 and 0.2°C. What we've seen is a rise of 0.9°C, in percentage terms the natural contribution could fall anywhere between 2 and 22%, the remainder being the anthropogenic component.

The above explanation is a simplified version of what actually goes on but I've used it because the results are broadly similar to those of the more complex calculations which take many other variables into account.

It's safe to say that upwards of 80% of the current warming is the result of human activities, the real figure is likely to be close to the 90% mark.

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As for how much warmer. Using the above figures, human activities have resulted in a net warming of between 0.7 and 0.9°C. This is the NET warming, some of our activities produce a cooling effect, if these are removed from the equation then anthropogenic warming falls between 0.9 and 1.2°C.

These figures cover the last 200 years, the rate of warming has increased quite dramatically, so much so that more warming has occured in the last 50 years than in the preceding 150 years. Currently temps are rising by an average of 0.0177°C per year (1°C every 56 years).

Answer 4

Scientists best estimates are 80-90%. Keith's extreme numbers of 62% or 98% are based on two longshot 5% chances coming true, a 0.25% probability. Not likely enough to worry about.

Here's a nice picture from the source below. This study is one of many that supports an 80-90% figure.

http://www.globalwarmingart.com/wiki/Image:Climate_Change_Attribution.png

This is not as uncertain as some people claim.

And the data shows it can't possibly be less than 50%, ie global warming is definitely mostly man made.

Right now the excess warming is about half a degree. The problem is that if it gets to 2-3 degrees (and it's heading there) the resulting changes to coastline and agriculture will be expensive in terms of dollars and lives. Details here:

http://www.reuters.com/article/scienceNews/idUSL052735320070407
http://www.ipcc.ch/SPM6avr07.pdf

If we started now we could hold it to more like one degree, which is manageable. Here's the plan:

http://www.spiegel.de/international/world/0,1518,481085,00.html
http://www.ipcc.ch/SPM040507.pdf

Answer 5

This is the big debate

On one side, you have recent minute changes in the average temperature globally which coincides with our current state of industrialization, and on the other there is the argument that (as recently as 22,000 years ago) most of north America and other continents were repeatedly covered by glacial ice which melted before man had any impact.

**********This portion has been edited as volcanos actually have a cooling effect. My comments were base on incorrect information from an admitedly right-wing source and was brought to my attention from another poster. My apologies for any inconvenience this might have personally caused. My attempt in this post was to be unbiased even though I am not fully convinced of the left's view on this topic. In all fairness, the poster completely ignored the fact that I do agree that we need to change our fossil fuel habits. *************


There is really no argument that mankind's activities have some impact on the global climate but how much and can we really make a significant difference in the current rise in global temperature is the 64 thousand dollar question.
Could seeking alternative fuel sources, reducing CO2 emissions, and reversing the global practice of deforestation be in our best interest? Of course they will as well as becoming vegan since cattle are a huge producer of greenhouse gases but will all of this make a huge difference on the climactic temperature shift? Who knows, this entire issue has become one of politics instead of the survival of our species.

... this answerer is willing to consider all sides of the issue but there is a consensus among many that only one side has any valid argument and some are willing to do so in a very disparaging manner which does not help the average (meteorologically) uneducated person to form a valid opinion on the subject. Shame on them all.


Additional comment,
Thanks for the link Patrick, that was very interesting reading. I did not intentionally lie, that's what happens when one parrots the "facts" given by un-credible sources. I was mistaken and do stand corrected. Can you dispel the myth about livestock emissions as well?
http://www.associatedcontent.com/article/131232/global_warming_carbon_dioxide_and_methane.html

Answer 6

Go rent the movie "An Inconvenient Truth".

It's not how warm the Earth is now (It's been warmer in the past). It's how fast it is changing and how much the human generated greenhouse gases are contributing to that extremely high rate of temperature increase.

Listen, the Earth's temperature has fluctuated quite a bit throughout it's history based on naturally occurring changes to CO2 and other greenhouse gas concentrations in the atmosphere (volcanoes etc.). The difference today is that on top of the natural swings in gas and temperature, human contributions have increased the gas levels many orders of magnitude (not doubled or tripled but multiplied by several thousand times).

Left unchecked, this will result in changes far beyond what humans have experienced in their existence and for which we are completely unprepared because of the speed that those changes will occur.

Answer 7

The impact of global warming is real, and yes, we are contributing to the problem. However, it isn't as simple as "the earth is getting measurably warmer". It has to do with many environmental changes. I suggest www.stopglobalwarming.org, and the websites for the documentaries on the subject "An Inconvenient Truth" and "The 11th Hour".
For those who say it is a "farce"-- if there is any possibility that we are harming our planet, and there are simple steps we can take to stop it, then why wouldn't we? Are we that lazy and selfish? I hope not.
And by the way, the science IS conclusive. Even the people who 7 years ago were trying to convince the public otherwise have acknowledged this. Wake up and do your research.

Answer 8

On average, they say it goes up about 1 degree every 100 years. It has been going up for hundreds of years. I believe it is up about 3-4 degrees from the last low point. Actually some areas seem to be going up and some not during certain periods. The temperature in my state has not gone up over the last 30 years or so. Not sure why.

Answer 9

Good question.

Since the end of the Little Ice Age almost 160 years ago, global average temperature has risen 0.7C.

The latest IPCC report, AR4, say that they are 66-90% sure that man contributes to this temperature rise. What that means is still a guess, and that is from the so called "consensus".

They have narrowed it down to the total man-made radiative forcing via the Greenhouse effect, but even this is unclear, since we don't have a precise knowledge of how much of our temperature is normally created by the greenhouse effect.

Answer 10

The temps are just now hitting triple digit in the south. So far this summer hasn't been all that bad.

Come and join our new green and global warming group

http://groups.yahoo.com/group/Green_Technology/