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    What's this?
Climate change arguments explained
What's the truth about man-made climate change? MNN weighs the evidence for and against the idea that humans are heating up the planet.

By

John Platt
Mon, Apr 11 2011 at 7:14 AM
 13

Related Topics:

Climate Change, Emissions, Fossil Fuels, Global Warming

Photo: NASA

Talking about global warming can be tricky. Everyone has an opinion, some of them more informed than yours. But what information is forming those opinions, and where does the truth lie? We looked at the various arguments for either side of the debate.
 
Arguments against the existence of man-made climate change:
 
1. Climate changes all the time. It has changed before and will change again.
Yes, climate changes are usually a natural occurrence, caused by changes in the sun, volcanoes and other natural factors. But historic shifts show us how sensitive the planet is to greenhouse warming from carbon dioxide in the atmosphere, and hint at how costly our modern CO2 surplus can become. Current atmospheric levels of CO2 are around 380 parts per million, up from about 320 ppm in 1945, while global surface temperatures during that time have risen 1.2 degrees.
 
Humans continue to pump CO2 skyward at an ever-increasing rate. According to the U.N. Intergovernmental Panel on Climate Change, CO2 levels are projected to rise beyond 400 ppm in just the next five years.
 
2. Scientists do not have a consensus about climate change.
Climate skeptics point to the Petition Project, where 31,000 scientists signed a petition saying there is no evidence that human-released carbon dioxide will result in a warmer atmosphere. Climate Depot has published another list of 1,000 scientists who disagree with man-made global warming claims.
 
But the peer-reviewed science does not support this. A study of papers mentioning global warming published between 1993 and 2003 revealed that 75 percent agreed humans were causing climate change, and the other 25 percent made no comment on the issue.
 
A later survey of more than 3,000 earth scientists — 97 percent of whom have Ph.D.s or master's degrees, compared with 28 percent of those signing the Petition Project — found that 97.5 percent of the scientists who had actively published research on climate change agreed that human activity was a significant factor in rising global temperatures.
 
And as the website Skeptical Science points out, "There are no national or major scientific institutions anywhere in the world that dispute the theory of anthropogenic climate change."
 
3. Scientists talking about climate change are just looking for grant money.
A common complaint levied against scientists who publish studies about climate change is that they are only in it for funding and are therefore creating a scare among the public. But as the website Logical Science points out, there really isn't a lot of money in science. In addition, published climate science is peer-reviewed, with scientists around the world constantly checking each others' work both before and after publication.
 
4. The sun is causing global temperature rises.
In 2004, scientists with the Zurich-based Institute for Astronomy presented a paper at a conference saying the sun had been more active in the prior 60 years than in the entire 1,000 years before.
 
Yet the study also concluded that after 1975, solar activity did not have a correlative effect on global temperature. In fact, the study says, "at least this most recent warming episode must have another source."
 
Numerous other studies have shown that solar activity in the past 50 years has declined while global temperatures have risen.
 
5. Global warming is good for the economy and for civilization.
As the Heartland Institute wrote in 2003, previous warming periods allowed humanity to build its first civilizations and made it possible for the Vikings to settle in Greenland.
 
In fact, climate change may create a few economic benefits. For example, the Northwest Passage is now ice-free a few weeks a year. This may allow for greater flexibility and speed (not to mention reduced costs) in shipping, allowing cargo ships to travel through the Arctic Ocean from Asia to Europe, rather than going south through the Panama Canal.
 
But a 2008 study published by the Organisation for Economic Co-operation and Development found that climate change "poses a serious challenge to social and economic development." Water resources will change, farming practices will need to be adapted, building codes will need to be rewritten, sea walls will need to be built and energy costs will rise, according to the report.
 
Arguments for the existence of man-made climate change:
 
1. Humans have caused the global rise in CO2 and other greenhouse gases.
Carbon dioxide levels are currently "25% more than the highest natural levels over the past 800,000 years," according to the Environmental Defense Fund. Deforestation caused part of that, with the rest coming from the burning of fossil fuels.
 
How can we know that oil and coal have contributed to this rise in CO2? Simple: Fossil fuel emissions have a different "fingerprint" than the CO2 released by plants. According to a study published in the Journal of Mass Spectrometry, you can identify the source of carbon emissions by the ratio of carbon-12 and carbon-13 isotopes. The atmospheric level of these isotopes indicates that a greater ratio of CO2 is now coming from fossil fuels than from plants.
 
2. Climate change computing models are good enough to trust and take action.
While no computer model is perfect, they are constantly getting better, and as Skeptical Science points out, they are intended to predict trends, not actual events. Each model must be tested to be proven.
 
One of the classic cases of a model proving to be correct was seen following the 1991 eruption of Mount Pinatubo, which proved James Hansen's model that an increase in atmospheric sulfate aerosols would actually decrease global temperatures by 0.5 degrees Celsius in the short term. The IPCC's models for Arctic sea-ice loss have actually been too optimistic, and ice loss has been more dramatic than predicted in the IPCC's "worst-case scenario."
 
3. Arctic sea ice is melting.
According to the National Snow and Ice Data Center, Arctic sea ice in February 2011 tied with February 2005 for the lowest level in the satellite record. Sea ice those months covered 5.54 million square miles, down from the 1979-2000 average of 6.04 million square miles. Meanwhile, temperatures were between 4 and 7 degrees higher than normal.
 
This doesn't mean that all ice is melting. Ice area in Antarctica has increased over the past three decades, but according to a study published last year in the Proceedings of the National Academy of Sciences, this is due to increased precipitation, mostly snow, itself brought about by greater levels of moisture in the air due to climate change. This stabilized the ice shelf, reducing the amount of melting it would have otherwise experienced from warmer ocean temperatures.
 
4. Ocean acidification is rising, caused by rising CO2 levels.
The oceans are a natural carbon "sink," meaning they absorb CO2 from the atmosphere. But as CO2 rises in the atmosphere, it also rises in the oceans, increasing their acid levels (pH) to a point that will be harmful to marine life. According to data presented at the second symposium on the Ocean in a High-CO2 World in 2008, ocean acidity has increased 30 percent since the Industrial Revolution, 100 times faster than any change in the past 20 million years.
 
As for the future, a 2003 study published in Nature found that "oceanic absorption of CO2 from fossil fuels may result in larger pH changes over the next several centuries than any inferred from the geological record of the past 300 million years, with the possible exception of those resulting from rare, extreme events such as bolide impacts or catastrophic methane hydrate degassing."
 
5. Ten of the last 12 years were the hottest years on record.
Skeptics say the hottest year on record was 1998, but as Skeptical Science points out, an "abnormally strong El Niño" transferred heat from the Pacific Ocean to the atmosphere. Meanwhile, only one of the three temperature records (HadCRUT3) showed 1998 as the hottest year, and that has since been found to have been a sampling error. More recently, 2005 and 2010 were tied for the hottest years since 1850, according to the U.S. National Oceanic and Atmospheric Administration, and all 10 of the hottest years on record have occurred since 1997.
 
Related climate change stories on MNN:
  • 6 ways humans can adapt to climate change
  • The secret role of clouds in climate change
  • How to discuss climate change with your uncle during the holidays
  • 7 surprising global warming deniers

You might also like:

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Comments: 13
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anonymous
ardou5 Oct 18 2011 at 8:22 AM

I don't understand the statement about plant causing CO2 - they absorb it.

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jplatt's picture
John Platt Nov 18 2012 at 11:56 AM

They absorb it while they're alive. All of that CO2 gets released when plants die.

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anonymous
Meme Mine Apr 13 2011 at 6:30 AM
The response from the thousands of consensus climate change scientists to Obama not even mentioning the climate crisis in his State of the Union Address was utter silence. And the scientist’s silence was on display when Republicans cut off American funding to their central research body, the UN’s IPCC. Now we see why the thousands of consensus scientists have vastly out numbered the protestors of 25 years of “the scientists all agree“ headlines. Finally, the world economy has lowered our
.... More
contributions of CO2 emissions for several years yet global CO2 levels keep rising? Avoiding serious climate hell should be a good thing. Maybe fear wasn’t sustainable as George Bush Jr. found out. We need system change, not climate change as continued support of the climate change mistake is hurting the planet, science and progressivism. Now there is serious talk of the tea party Republicans charging those in Academia and leading news editors with TREASON for leading us to another Bush-like false war based on false evidence. If Climate Change were a real emergency and scientific consensus was real, the scientists would be acting like it, not cashing the remaining grant checks. The scientists if the emergency were real would be all over the media in person, warning us of the urgency of CO2 mitigation action. Now the media makes up it’s own climate change stories in place of the silence from the mysterious army of consensus scientists. And don’t forget that scientists also produced cruise missiles, cancer causing chemicals, land mine technology, nuclear weapons, germ warfare, cluster bombs, strip mining technology, Y2K, Y2Kyoto, deep sea drilling technology and now climate control. Scientific consensus was not real and these mystery saints of goodness were not saints. It was all a media illusion. Scientists made environmental protection necessary in the first place when they supposedly polluted the planet with their chemicals and cancer causing pesticides. How ironic is that, considering we bowed like fools to our Gods of science for 25 years of “unstoppable warming”. To condemn billions of children to a CO2 death just to get them to turn the lights out more often was unforgivable and history is watching.
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anonymous
Meme Yours Apr 29 2011 at 8:54 PM

But this article was written with you in mind.

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anonymous
John Dodds Apr 11 2011 at 4:39 PM
Your arguments are not scientific to stand the test of time. You Cherry pick data to justify your preconceived notions. Your article is absurd. and full of false assumption. Specifically Item 1. Climate changes all the time. This is a fact. Ice core data shows the variations. It was warmer in the Viking Era around 1000AD, It was warmer in 100BC the Roman and Han dynasty era. It was warmer in 1350 BC. Warmer temperature correspond to civilization highs. Colder temperatures correspond to the falls
.... More
of civilizations. Quoting measured temperature for which data only goes back 150 years is misleading and ONLY uses data for the latest warming period. It ignores older data. item 2. Consensus. BULL. There are disputes about the conclusion. There is even a dispute about the Arrhenius data used as the original source of the conclusion that More GHGs means more warming. Every day when the sun goes down and less energy comes in, the temperature goes DOWN, in spite of man adding more GHGS or CO2. That fact alone proves that more CO2 does NOT cause more warming. It is the number of energy photons that cause the warming. Arrhenius predeveloped his conclusion without looking at the daily reality. Just like your article is doing. I have a theory about anthropogenic climate change. Hansen says when you add more GHGs they ALL generate more warming. He says more CO2 means more water vapor (feedback) and ALL the water vapor undergoes the greenhouse effect. BUT if daily experience shows that the number of photons dictates the temperature then ALL of the CO2 and Water Vapor does NOT generate a greenhouse effect. There are GHGs left over as excess that do not generate warming. Aren't there GHGs in the ocean that are not warmed? The only way for that to happen is if all the photons are in use, & there are excess GHGs left over. IN other words only some of the man generated CO2 and some of the subsequent water vapor contributes to the GHE. IN other words Hansen's computer program is wrong. It is not valid. 4. Yes there is no correlation between the sun & global warming. There also is ABSOLUTELY no correlation between CO2 and warming. Every night in fact, the CO2 goes up & the temperature goes down. There MUST be another source of energy /photons into the Earth. The paper Gravity causes Climate Change" in www.scribd.com identifies gravity as another source. As Jupiter gets closer to Earth, it gets warmer (1998, 2010) as potential energy is released to become heat energy AND as more gravity causes more waves & wind and friction and heat. Gravity & potential energy has been totally ignores in the conventional global warming computer programs. 5. Global warming corresponds to civilization highs. Global cooling corresponds to periods of less activity & more suffering (ice ages, the little ice age, etc Arguments for the existence of Man Made change. 1. NO. Humans have cause the increase in the CO2. It is the number of energy photons that combine with the excess of GHGs that causes the warming. More photons means more warming, every morning. Fewer photons causes cooling every night. Since there is excess GHGs over the number of photons, then the amount of GHGs has no impact on temperature. It is impossible for CO2 to create energy or heat. You have to have more energy photons to do that. 2. The current computer models are pure garbage. They ignore the force of gravity. They assume that all GHGs cause warming, when in fact all the GHGs in the ocean do NOT.. They assume that only the water vapor produced in response to CO2 causes warming, while ignoring the water vapor GHGs already in existence in the air. The current computer models are so deficient they should be totally ignored. 3.Yes the arctic sea ice is melting. SO What? MOST of Earth's history has NOT has ice caps at the poles. It is only in the last million years that they have existed. Normal is no ice. 4.Ocean Acidification is rising. Yes so what. The PH has gone up by .1. It varies by much more than this from location to location in the ocean. 5 !0 of the warmest days on record were the hottest Garbage. Ice cores show hotter days in 1000AD, 100BC, 1350 BC and by as much as 2 degrees C. The 10 hottest days are ONLY in the last 160 years since we have been measuring. If we are in a 500 year warming cycle, you would expect the most recent to be the hottest. IF more CO2 means more warming, why was 1999 cooler than 1998? Why was 2006 cooler than 2005? The real reason is that Jupiter was further away & hence contributed less energy from gravity, NOT because of CO2 which has gone straight up & so does NOT correlate with the temperature. Your article is not valid. It should be ignores as propaganda.
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anonymous
Leigh Bunting Apr 11 2011 at 6:30 PM

OK John, you have obviously done a lot of research and thinking. Have your theories been published in peer-reviewed papers? Can you please list your published papers? Can you please list your career information and qualifications so I can keep track of your illustrious career? To call Hansen's computer models wrong is a very bold step. Can you please advise what modelling systems you use?

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anonymous
Guest Nov 17 2012 at 10:36 AM
Leigh, if you're dedicated to a scientific approach, then you should be able to refute the scientific arguments on the following site one by one, rather than falling back on the computer model, and making an ad hominem argument directed at John's "illustrious career": http://www.petitionproject.org/gw_article/Review_Article_HTML.php Speaking of ad hominem arguments, another is this site's suggestion that the petition project's science is inferior because only 28% of the scientists signing the petition
.... More
have advanced degrees, compared with 97% of those publishing research. If one places that much faith in advanced degrees, and is honestly seeking to weigh arguments on both sides, one will focus on the arguments advanced by the 28%. Further, to compare 97% of published papers to 28% of people signing a petition is simply juxtaposing two completely unrelated numbers and saying "see, ours is bigger than yours." Further, research papers are peer reviewed, and the implication here is that peer review guarantees the truth of the conclusions contained therein. It assumes that no individual's career (not money, not funding, but career) is dependent on drawing a particular conclusion supporting man-caused global warming, and that any potential bias is completely mitigated by the scientific approach. In fact, this is not true, and for evidence I'd point you to the Decline Effect. The Decline Effect is a marked tendency for scientific claims to receive decreasing scientific support over time: http://en.wikipedia.org/wiki/Decline_effect_(article). This isn't a problem with the scientific method itself, but with humans, who are inherently fallible. Therefore some humility is in order, all around. Keep in mind that those who argue against man-caused climate change are anti-establishment in the scientific sense, and probably have more to lose than gain. This is the only valid rhetorical argument that I know of for making an examination of the person making a claim: who has something to lose by making their argument? Still, I'd circle back to their scientific arguments themselves and ask that you refute them one by one, or else open your mind, rather than falling back on the argument that the computer model is infallible.
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anonymous
Bomber_the_Cat Apr 11 2011 at 2:51 PM
Sorry, I got stuck at point one. " Historic shifts show us how sensitive the planet is to greenhouse warming from carbon dioxide in the atmosphere" No they don't! What evidence is there for this ridiculous unscientific statement.? If you get the first step wrong, then everything else that follows is going to be wrong too, so I didn't bother to read on.. Unfortunately, this is the sort of nonsense that used to pass without criticism, but now, as the greatest scientific scandal of all time collapses,
.... More
it no longer does.
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anonymous
Michael Jones Apr 11 2011 at 2:14 PM
From the comments generated here, snap out of it! Hey, look at number 4 in the for section (I know you deniers skipped over it), for that reason alone we must cut back on carbon emissions! I know, we don't live in the ocean, so it is no concern to us people. Boy, this is getting real tiresome. Oh, Dr. James Hansen has been awarded the 2011 recipient of the Klopsteg Memorial Award from the American Association of Physics Teachers. I'm sure if there was doubt about his work on Global Warming this would
.... More
have be given.
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anonymous
Harry Dale Huffman Apr 11 2011 at 12:20 PM
Nearly 20 years ago, the Magellan spacecraft took detailed data on the temperature and pressure profiles of the Venus atmosphere. Comparison of the temperatures in the atmospheres of Venus and Earth prove there is no greenhouse effect due to CO2 on either planet: Venus: No Greenhouse Effect Climate scientists like James Hansen should have done this simple comparison nearly 20 years ago, rather than promulgating a political agenda based upon a false hypothesis, which has suborned all our scientific
.... More
institutions and become a false dogma worldwide. It is runaway dogma, within science itself, that now threatens mankind, not runaway climate change.
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anonymous
Harry Dale Huffman Apr 11 2011 at 12:24 PM

... Climate scientists like James Hansen should have done this simple comparison nearly 20 years ago, rather than promulgating a political agenda based upon a false hypothesis, which has suborned all our scientific institutions and become a false dogma worldwide. It is runaway dogma, within science itself, that now threatens mankind, not runaway climate change.

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anonymous
TA Apr 11 2011 at 10:54 AM
I was very dismayed to see another climate change article written and not one word mentioned about methane or black carbon (soot). These are two GHG's we can address immediately (with very little resistance politically or economically) and it would have an immediate impact on our environment. It would far outweigh whatever gains we may get by curbing CO2. I wish people who care about this topic would shift their focus to this. Also, you might want to look up 'fossil water' and research that topic
.... More
and ask yourself why are we not monitoring how much of that is being released back into the atmosphere every year. There is no solid number and it would have a much greater impact (short-term) on global warming than any GHG would.
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anonymous
mememine69` Apr 11 2011 at 5:37 AM
There is now serious talk of getting the government to issue charges of treason (typical teapartyer term) to those in academia who knowingly lead us to a false war against climate variation. And considering Obama chose not to mention the “ global climate crisis” in his state of the union speech, plus the fact that the IPCC had it’s American funding eliminated by the senate, one can see how damaging and costly and pointless this all is now. Did our saintly scientists march in the streets in
.... More
protest and demand time on CNN for Obama bailing and having funding cutoff? This IS the worst possible emergency EVER! Climate Change wasn’t “environmentalism”, it was a 25 year old death threat to our children and marching orders for mindless ideologues. Real planet lovers were glad it was a criminal exaggeration of disco science and fear mongering media and thus averting an unspeakable end of the world by unstoppable warming. It was a sick and twisted mistake and history is cursing us all for this madness.
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