So to what extent is global warming caused by humans?

Question

So to what extent is global warming caused by humans?

Answer 1

We humanoids are changing the makeup of the atmosphere which surrounds this planet.  The changing of the chemical soup we call air is retaining more heat.  

    "yes we can affect the weather" as we spew the vast amounts of CO2 into the atmosphere with our need for transportation and electricity(from coal fired generators) and we continue to cut down the forests that convert the CO2 into carbon and oxygen.

   To get a perspective....if the earth was the size of a basketball, the atmosphere is the thickness of saran wrap.

Answer 2

For the latter part of the 20th century, in the realm of 70 - 90% (since the largest estimates of solar induced warming is 10 - 30%).

Answer 3

I don't think anyone really knows for sure - but do we really need to prove it  before we start to do anything to try to control it? Surely it is best to assume that we are indeed contributing to climate change - and to change our energy habits just in case?

If it turns out that we can't stop it - then so be it. At least we can say to the next generation that we tried!

Answer 4

Bob, 80-90% by humans, come on, lets get real. Take your hat off and let the sun warm up your brain.

Answer 5

80%-90%

Answer 6

That's a debate that can go on forever. It doesn't change the fact that 100% are suffering because of it. The question is how to slow it down before we've lost everything.

Answer 7

activities of humans responsible for global warming:

deforestation,mining,nuclear power,rockets to space which create ozone holes,overuse of power.

Natural causes:

volcano,forest fire, outer space debris entering to our atmosphere.

so humans are 85% responsible.

Answer 8

0%.  

Repeat after me:

HUMANS CANNOT CONTROL THE WEATHER!

Answer 9

we do it all by ourselves, sawing of the limb of the tree we sit on.

Answer 10

There are many basic scientific facts which can only be explained if the current global warming is being caused by an increased greenhouse effect due to carbon dioxide accumulating in the atmosphere from humans burning fossil fuels.

For example, the planet is warming as much or more during the night than day.  If the warming were due to the Sun, the planet should warm a lot more during the day when the Sun has influence.  Greenhouse gases trap heat all the time, so they warm the planet regardless of time of day.  Another example is that the upper atmosphere is cooling because the greenhouse gases trap the heat in the lower atmosphere.  If warming were due to the Sun, it would be warming all layers of the atmosphere.

http://answers.yahoo.com/question/index;...

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

http://www.epa.gov/climatechange/science...

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/62902...

http://www.pubs.royalsoc.ac.uk/media/pro...

A recent study concluded:

“the range of  [Northern Hemisphere]-temperature reconstructions and natural forcing histories…constrain the natural contribution to 20th century warming to be <0.2°C [less than one-third of the total warming].  Anthropogenic forcing must account for the difference between a small natural temperature signal and the observed warming in the late 20th century.”

http://www.pnas.org/cgi/content/full/104...

You can see this in the third graph here, where the dotted lines are just from natural causes, and the full lines are natural + human causes:

http://www.pnas.org/content/vol104/issue...

If that’s not enough to convince you the Sun isn’t responsible, consider the fact that no scientific study has ever attributed more than one-third of the warming over the past 30 years to the Sun, and most attribute just 0-10% to the Sun.

http://answers.yahoo.com/question/index;...

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/Milankovitc...

http://www.sciencemag.org/cgi/content/ab...

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 150 times more CO2 than volcanoes annually

http://volcano.und.edu/vwdocs/Gases/man....

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...

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:Clima...

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

Answer 11

none in a measurable state, there are more species of animal on the planet than humans

Answer 12

The system is to complex to begin to answer your question. Look up some of my old answers.

Answer 13

Humans also caused the latest eclipse...

Answer 14

99% by human activity,

Answer 15

80-90%.

Here's a study that was designed especially to answer this question.

Meehl, G.A., W.M. Washington, C.A. Ammann, J.M. Arblaster, T.M.L. Wigleym and C. Tebaldi (2004). "Combinations of Natural and Anthropogenic Forcings in Twentieth-Century Climate". Journal of Climate 17: 3721-3727

summarized at:

http://www.globalwarmingart.com/wiki/Ima...