Dr. Richard Nolthenius - Program Chair of Astronomy, Cabrillo College
The climate debate - Is the strong global warming of the past ~60 years due to human activities or not? But wait... is there really a "climate debate"? No. Not among climate scientists themselves. Global warming is strongly supported by the evidence to be human-caused. The idea that human-generated CO2 can change climate significantly dates back over 100 years. By 1990, data, computer modelling, and theory were solid enough to leave little doubt that human-generated fossil fuel emissions were changing climate and that it would accelerate. Since then, the widening disagreement between reality and climate models which neglect human causes has caused growing alarm and consensus that dramatic and urgent action is needed. More recently, 98% of working, publishing climate scientists support the conclusion that global warming is real (i.e. not just a wiggle in noisy climate records, or "natural variation") and caused by human activities, mainly though fossil fuel burning, according to this analysis published in the Proceedings of the National Academy of Science (Anderegg et.al. 2010) . But, you say, we hear all the time on the news how controversial the issue is and it seems scientists are arguing fiercely about what is causing climate change - isn't it obvious there's a genuine debate on global warming's cause? No - the problem is that there are well-funded lobbying efforts by oil and mining corporate interests to get the public and the politicians to believe there's a big scientific controversy, as a way to stall policy changes which threaten their profit streams. While there is a very active continuing research effort to clarify key climate processes, including modelling clouds and their feedbacks, the evidence strongly indicates that while these refinements will improve the error bars, they will not change the verdict. Depending on how that goes, the business-as-usual scenario will, by the end of the century, vary from being very bad, to being truly disasterous. There is no reasonable possibility that they will exonerate humans as the cause of the rapid warming that we're seeing. And therefore, that it is up to human beings to change, if they want to avoid disaster. I will justify that statement in this website.
If this were a resource page on purely astronomical understandings, there'd be no need to delve into politics and junk science. There's no corporate interests who feel threatened by what astronomers discover or conclude. Not so in climate research. Unfortunately, students cannot simply accept on trusting faith that what they hear in the media, or even in some classrooms, can be taken at face value.
I'll organize this website as follows: First, examing the politics and its connection to the large amount of nonsense out there in the media, then the claims by those attempting to absolve human responsibility for global warming, and finally the evidence which convinces climate scientists that global warming is real, it's extremely serious, and it's caused by us.
AGW = anthropogenic global warming = global warming which is caused primarily by human activities, a useful abbreviation in what follows.
1. The Politics of Climate
2. Debunking the AGW Denialist claims, and some Denialist Tactics
3. The Key Evidence That Global Warming is Human-Caused
4. What is to be Done? Strategies
Growth rate of CO2 in parts per million per year, with 10 year averages included (horizontal bars). I've added the economic recessions for the past 50 years, which correlate well with drops in the rise rate of CO2. This is most dramatically seen in the "oil-shock" recessions of the Arab Oil Embargo of '74, and the first Gulf War in '91, which particularly affected the availability of oil. The correlation is obvious.
We have confirmation that the observed rapidly rising CO2 levels are coming from fossil fuel burning from the known emissions rates, from the unique carbon isotope ratio found in oil and coal laid down hundreds of millions of years ago (Ghosh 2003, and for the layman here), from the observed signature of economic recessions in the CO2 rise rates (see figure at left), and other data. We know the physics of the Greenhouse Effect with very high precision, we know the distribution of CO2 around the planet and that it is throughly mixed on a short time scale, and that the physics of the greenhouse effect leaves no doubt that man-made GHG (greenhouse gases) will cause warming of the troposphere and cooling of the stratosphere at levels consistent with real observations, even without complex climate models. We know that study after study has found that humans account for ~100% of the global warming over the past ~60 years (see graph at left). When the new IPCC AR5 report is issued at some point in 2013, summarizing the best science of the past 5 years on climate, expect to get a significantly more ominous human-caused climate attribution and future scenario than from the IPCC AR4.
Net human and natural contributions, in percent of total, to the observed global surface warming over the past 50-65 years according to Tett et al. 2000 (T00, dark blue), Meehl et al. 2004 (M04, red), Stone et al. 2007 (S07, green), Lean and Rind 2008 (LR08, purple), Huber and Knutti 2011 (HK11, light blue), and Gillett et al. 2012 (G12, orange). Note that natural contributions in most studies are actually slightly cooling the planet, so that human-caused global warming is actually stronger than 100% of the warming that we observe.
We know that the denialists have provided not a single theory shown to be consistent with the observations, nor even an idea which pretends to be an explanation for what we have seen. They attack by seeding doubt, and they attack the integrity of climate scientists and even the process of science itself. At best, they propose ideas or mechanisms which would affect modelling and the exact level of error bars on graphs, but no theory predicting what we, in fact, see. We know that many millions of dollars of corporate money is being funneled to climate denialists and that their media and political connections have succeeded in dis-informing lay people, politicians, and even second-rate teachers who should know better, playing on their psychological tendencies. We know that this is especially prevalent in the United States, and that people in Asia and Latin America, for example, are much better aligned with the scientific consensus. As of 2009, only 36% of average Americans believe that global warming is caused by human activities, from a Pew poll. We know that there is already further warming of 1 degree Fahrenheit "in the pipeline"over the coming decades which will happen even if, against the social inertia, we stop all CO2 emissions instantly, due to the well understood thermal inertia of the ocean and its decreasing ability to absorb CO2 with increasing temperature. And we know that the relatively mild policy proposals so far discussed, including Kyoto, are inadequate to prevent economically and environmentally devastating consequences. We know that even these proposals can't get any political traction, due to the efforts of denialists (example: the CRU email theft just before the Copenhagen Climate Summit , and see the denialism of the Republican candidates of the 2010 election). The Copenhagen Climate Summit, thanks in part to the efforts of climate denialists, was a dismal failure. Even the one "accord" agreed upon, that we must confine total global warming to no more than 2 degrees Celsius, is derided by scientists as far too much ("2 C is the boundary between dangerous and extremely dangerous climate change" A. Bows; Tyndall Center for Climate Change Research), and yet at current emission rates, by 2028 we will have already used up our entire allotment (~565 billion tons of CO2 emissions), which can have some hope of keeping us under 2 C. This represents only 1/5 of proven oil reserves. Said another way, if we continue on "business as usual" till 2028 and then STOP ALL EMISSIONS PERMANENTLY, we will have commited to 2C of warming and that warming would be itself permanent (as we'll see). 2C is more than 1/3 of the warming that happened emerging out of the last great Ice Age.
We need immediate and severe reductions in CO2 emission, a fact which is in such strong conflict with the desires of the Third World and Asia to adopt the conspicuous consumerist lifestyle they envy from the West, that it may well take a whole series of catastrophic events spaced closely enough that they do not exceed our shrinking attention span - events unequivocally tied to global warming - before civilization will take the drastic steps required to prevent the worst consequences. Even more serious than climate change is the tragedy that CO2 is inflicting on ocean ecosystems due to CO2-induced acidification (links here, here, and references therein).
Maybe this is a good place to repeat something I have, for 26 years now, told all my Astro lecture classes at one point or another - Nolthenius' First Law: People Learn the Hard Way. Most (a voting majority certainly) are unable to make real and compelling enough within their own minds what the difficult truth is, and to support the necessary action. They will eventually commit to serious action - but only after it's far too late; that is the science of time scales, and the very unfortunate time scale for climate forcing and response, as we'll see.The Larger Problem - Living Beyond the Carrying Capacity of The Earth
Meanwhile, as the American public and politicians appear unwilling or unable to see through the fog financed by the oil and mining industry and face up to human responsibility for global warming, the rest of the world moves on. China, only recently having elevated itself out of Third World status, is already leading the U.S. in all measures of clean energy technology development and use, and by a significant margin. China is hardly a model world citizen, but they are not indulging in the self-deception that we are, here in the U.S.
All of human civilization, beginning with paleolithic man emerging from the last Ice Age, has taken place in this time frame, and enabled by a stable climate that allows consistent growing zones and building of civilization infrastructure. Now look at the man-made carbon-induced climate change that has started. Taken from Marcott et.al. (2013), and described for the layman here
A Few Degrees Warmer - So What?
You may think - "What's the big deal? Heck, I don't even know if I can tell when it's a couple of degrees warmer. Temperatures go up and down more than that every day of every year. Maybe I'll have to crank up my air conditioner a notch during summer, maybe we'll have to say good bye to a few species. It's not a disaster (After all, Richard Lindzen says so!)". What this naive thinking fails to grasp is two things. First, that the change in temperature is held consistently, not oscillating as in the daily or seasonal cycle with no net change in the average. A consistently held temperature rise, even when small, has very strong consequences. Second, that the world is adapted to a global climate which is disappearing far too rapidly - species cannot adapt when change happens this quickly. Species adapt when changes happen slowly over thousands of years or longer. When change of this magnitude happens in decades - species instead go extinct. A few degrees, held permanently, will melt all the ice of the poles, will cause mass die-offs of present forests and crops, will melt Arctic lakes and tundra with large reservoirs of methane. Methane from the melting permafrost is now calculated to add fully another 30% or more to greenhouse forcing, beyond what has already been assumed in the IPCC AR4 of 2007 (UN report 2012). A warming ocean has the very real (but still poorly understood) possibility of destabilizing vast continental shelf methane hydrate deposits in a runaway positive feedback loop, rapidly escalating warming still further. Another dangerous positive feedback is the thawing of the vast carbon stores in the permafrost. This new study in 2013 shows (Vaks et.al. 2013) that this begins at a temperature of only 1.5C above pre-industrial levels. We are already halfway there, and the other half is guaranteed "in the pipeline" through thermal inertia, even if we stop emissions today. The accelerating temperatures from this will be further quantified no doubt later in 2013. But clearly there will be devastating effects. Countries will lose their most valuable and populated property - coastal property. You may say - there'll ALWAYS be coastlines, so what's the big deal? But as sea level rise accelerates, it makes it very difficult to count on shoreline positions stable enough over time to hold their economic value. A recent paper by well-regarded geophysicists (Raymo and Mitrovica 2012 in the journal Nature) indicates that, based on the observed sea level rise during a comparable temperature rise such as we are seeing in the 21st century, we may see a sea level rise of 31 feet above today's level. That will devastate most of the Earth's great cities. Countries like Pakistan (a nuclear power, and not a very stable one) will lose a high fraction of its agricultural land, and a significant part of their entire country. Some island countries will simply be swallowed by the ocean. Crops will fail as rain patterns change. Wildfires will become larger and more widespread, yet another positive feedback further adding CO2 to the atmosphere. Here in California, droughts will become more common and more severe. This is confirmed by the observations that the Hadley Cell boundary (which now borders California's southern edge), marking the latitudes of descending drying air that cause the Earth's great deserts, has widened by ~5 degrees of latitude (about 300 miles) since 1979, corresponding to the period of rapid CO2-induced climate change (Johanson and Fu 2009). Drought in the mid latitudes is and will continue to fuel more fires and the ash from these fires is finding its way to the ice caps, especially worrying is wildfire ash and coal plant pollution dirtying Greenland, whose albedo is dropping, accelerating the melting of the ice. Rapidly rising CO2 will continue to be absorbed into the ocean much faster than it can be taken out by natural processes, raising its acidity and ruining the ability for calcium carbonate to form, which is the basis for a vast array of sea life which depend on this chemistry. The pH of the oceans have changed more in the last 150 years than in the previous several million years. The effects on all calcarious ocean life forms is serious. This includes corals which form the habitat for 1/4 of all marine species at some point in their life cycles. Already we are seeing mass die-offs of coral reefs. Half of one of the world's great heritage sites - Australia's Great Barrier Reef - is already gone, due mostly to weakened and bleached coral combined with increasingly severe storms. Prior to the 1980's coral bleaching there was unknown. Now, it is common, due to rising ocean temperatures. Corals can only survive in a bleached state for a few weeks, Even using the overly conservative 2007 IPCC scenarios, by mid-century the oceans will be too acidic for the survival of coral reefs (Lang 2007), and they will disappear (Silverman et.al. 2009). In CO2 conditions corresponding to the end of the century with "business as usual", experiments at the Great Barrier Reef show corals will be gone (De'ath et al. 2013).At higher acidifications, all carbonate-based species will perish. Note that 45-70% of the oxygen in the Earth's atmosphere (Fenicle 1983, and here) is produced by marine phytoplankton. Here is a good introduction to anthropogenic CO2 and the dire consequences of ocean acidification. Here is an introductory video program on ocean acidification designed for the general public. There are already serious pH-induced reproductive failures among shellfish happening now. The pH in the Puget Sound of Washington, uncorrelated with any local drivers, has plunged (acidified) from 8.3 to 7.7 in just the past decade (Wootten 2013). Freshwater systems face a bleak future as well. The Great Lakes are predicted to degenerate into a vast toxic soup of deoxygenated water and surface scum, as indeed is already beginning in the most fish-rich (historically) and southern-most of the lakes; Lake Erie (Michalak et al. 2013). Climate change is rapidly destabilizing our ability to provide food for a still growing population. Already, revolutions are beginning, caused by famine. New studies (2012) by integrative biologists provide evidence we are rapidly heading towards a world in which it will be very difficult for us to live (versus just sending off to extinction many of our fellow creatures which we deem not sufficiently economically useful to us). And exactly how sensitive is climate to a doubling of CO2 levels? Pagani et al. (2006) argue that to explain the Paleocene-Eocene Thermal Maximum may require a much higher sensitivity of global temperatures to a CO2 doubling than has been conventionally assumed. This argues that positive feedbacks (clouds most likely) are more powerful than the base case assumes. This conclusion is also consistent with the work of Fasullo et al. (2012), who finds that it is the most "alarming" climate models which do the best job of predicting what we have already seen. (see an interview with Fasullo on this work here).
What will be the response of civilization as this rapid ecological change accelerates in coming years? World wars have started over much less. Fighting over desires or "status" is one thing.... perhaps tempers can be calmed.. But fighting over basic food, water, and the very existence of the land you live on, is quite another. The 6 C global temperature rise which is now a serious prediction for the end of the 21st century, is larger than the global temperature difference between the depths of the last great Ice Age (5 C), and the current warm interglacial, before human-caused global warming. This is happening in a mere century rather than over tens of thousands or millions of years, as in past climate changes.
And these changes will continue for thousands of years. The higher global average temperatures we cause now, will remain high. They will not go back down - even if we stop all carbon emissions today - temperatures will not drop for thousands of years. (Solomon et.al. 2009). Pause, and let that sink in. A few degrees is devastating.
A Final Comment
The first warnings of anthropogenic CO2-induced global warming date back fully a hundred years. One hundred years! The evidence for human-caused global warming was strong enough in the late 1980's to be "settled" for strong policy changes. Denialism and oil/mining lobbying have combined with a science-ignorant American public (and alarmingly poor public education) to stonewall the hard policy needed to drastically reduce carbon emissions and save what we can. Denialists continue to claim that strong action is premature, that more science is needed, that it's too costly to our lifestyle to think about significant reductions in CO2 emissions until the "science is settled" (it is settled: Humans are responsible and only we can take action - where have you been?), and worse - that scientists are liars, group-think'ers akin to religious zealots, and conspirators. Consider this cautionary tale: Merrill Lynch in 2008 used a few million dollars in extra bonuses to motivate its own brokers to buy billions of dollars of Merrill Lynch-created CDO's (collateralized mortgage debt obligations) which the wider market judged to be of both very low-value and very high-risk, just in order to move these CDO's out the door. This essentially was committing suicide - just a few years ago, Merrill Lynch, through its own short term greed for a few million dollars, destroyed itself - a 100 year old financial institution once worth tens of billions of dollars. In the same way, the oil and mining corporations appear just as willing to do almost anything to keep just one more quarter of big profits coming in, even if it means long term disaster for our children and all future generations. Climate scientists are receiving threats of bodily and other harm. There is the prospect of McCarthy Era -style inquisitions of climate scientists by the Republican-dominated House of Representatives (and here). The Arctic Ocean is projected to be only a couple of dozen years away from losing the last of its permanent ice, with dire consequences for the albedo of the Earth and further warming. We are in the midst of the 6th great Mass Extinction since life began on Earth, this one caused by humans - the Anthropocene Extinction it is being called, with approximately half of all species of life on Earth predicted to go extinct by the end of this, the 21st century - half, or more. Given the overly conservative estimates on the loss of polar ice in the (2007) IPCC AR4 and the much faster environmental damage which observations are showing (see bottom of this page), many in the climate science community are afraid it may already be too late. That the tipping point has already been passed. If so, what a stupid and tragic legacy we are leaving to all future generations. Climate scientists are, privately, angry and appalled at the reaction to their work. Biologist that I know personally are so bitter that they have expressed the sentiment that we deserve the fate which we ourselves are going to suffer, including likely massive loss of life. Future generations will look back on us with contempt. To stumble into a tragedy is one thing - but this tragedy we have known was in the making for decades, while policy makers, corporate leaders, and most unforgivable of all - even some educators, decided their own agendas were more important than communicating the weight of evidence for what is happening, and what is coming.
From the IPCC AR4 document, 2007. More recent studies show these projections are very likely significant underestimates of the severity of warming in the future.
From Wigley & Weaver (2010) with explanation here. The red curve is climate change if all greenhouse gases are kept at 2010 values - warming continues for at least 200 years (essentially the purple curve from the IPCC graph at left). The blue curve is if we stop ALL GHG emissions today - the result is that we only keep temperatures constant - they do NOT fall. This is a vital point which seems unappreciated in the popular press. The naive notion that if you just stop doing "bad things", then the world will stop punishing you - is false. We need to REVERSE what we have done - immediately.
Update Dec 17, 2012
Significant parts of the current draft of the new IPCC AR5 (assessment report #5 since the IPCC was created over 20 years ago) have just appeared ahead of full publication anticipated in 2014. They confirm the key points of what I've presented on this website (no surprise). Yet climate denialists continue with their standard behavior - ignorance of basic science, shrill slander against scientists, and ideology-driven anti-science spin. See the latest IPCC graphs and the nonsense from denialist bloggers here, and the response of the IPCC author/scientist here. Still, the leaked draft of AR5 remains significantly more conservative than is the actual science of the past 6 years since the previous IPCC AR4. This is, after all, a report that gets tinkered with by not only the scientists, but also the political leaders - the IPCC is a United Nations sponsored entity, and the largest carbon emitters are also the countries with the largest contingent of IPCC scientists. Nevertheless, I continue to give the IPCC great credit in persevering with the science they DO manage to get past all the desks along the way to publication.
-- See the powerpoints and other web material I have assembled for my course Astronomy 7 - "Planets and Climate", which has a great deal of material on current climate change on Earth
--Here's a good set of video programs covering in concentrated form the scientific case for human-caused global warming and a close look at the attempts to discredit human-caused global warming, from a prominent science writer.
--A set of videos from the National Academy of Science, for the layman, on the evidence for human-caused global warming
--Here's a lecture ( from 2011; 1hr 20min) by Professor Richard Milne at Univ. Edinburgh on critical thinking, climate change, and denialism. Just ran across this in Fall '12 and haven't listened to it yet. Hopefully it's good.
--Earth: The Operator's Manual (PBS program hosted by Richard Alley)
--A UCAR module for the scientifically minded layman and weather people, on climate modelling
--Prof. David Archer's Univ. of Chicago course Phy Sci 134: "Global Warming" in a series of mp4 lectures.
and below as a series of video lectures for the non-science major. Note, these had been on YouTube but have been removed, and the higher resolution versions are freely available at the University Chicago link provided. I would suggest downloading them and then using your favorite mp4 player to watch them...
0 - Global Warming in Geologic Time (1hr 10min)
1 - Intro (11min)
2.2 - Heat and Light (50min)
2.3 - Blackbody Radiation and Quantum Mechanics (44min)
3 - Our First Climate Model (46min)
3.2 - The Greenhouse Effect (43min)
4.1 - What Makes a Greenhouse Gas? (45min)
4.2 - Greenhouse Gases in the Atmosphere (45min)
5.1 - What Holds the Atmosphere Up? (51min)
5.2 - Why It's Colder Aloft (45min)
6 - Wind, Currents, and Heat (50min)
7 - Ice and Water Vapor Feedbacks (35min)
7.2 - Clouds (48min)
8.1 - The Weathering CO2 Thermostat (37min)
8.2 - The Lungs of the Carbon Cycle (47min)
9.1 - The Battery of the Biosphere (43min)
9.2 - Coal and Oil (49min)
9.3 - Oil and Methane (44min)
10.1 - The Carbon Cycle Today (34min)
10.2 - The Long Thaw (41min)
11.1 - The Smoking Gun (46min)
11.2 - The Present in the Bosom of the Past (44min)
12 - Six Degrees (46min)
13 - Hot, Flat, and Crowded (13min)
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