# Global Warming... **URL:** \ **Category:** Great Debates\ **Created:** [October 19, 2004, 5:18pm UTC](https://boards.straightdope.com/t/global-warming/270062 "2004-10-19T17:18:23Z")\ **Posts on this page:** 14\ **Page:** 4
**Author:** ![Rashak\_Mani](https://avatars.discourse-cdn.com/v4/letter/r/ea666f/32.png) [@Rashak\_Mani](https://boards.straightdope.com/u/Rashak_Mani)\ **Post date:** [October 24, 2004, 2:14am UTC](https://boards.straightdope.com/t/global-warming/270062/61 "2004-10-24T02:14:20Z")
> [@Loopydude](#): > > This is the only rational way to approach the issue. > > In my parents’ home town, up in the hills of Maine, I can remember many winters when the snow would get so high that you couldn’t see out the ground-floor windows of my grandparent’s house in January. Now sometimes I go there in January, and there’s no snow at all. For the past twenty years, there’s never been more than two feet of snow on the ground, even after a big storm. I’m only 34, and my childhood memories of northwestern Maine look like a mini ice-age by comparison to today. It’s not just my imagination, either; everyone I’ve ever spoken to acknowledges it, and it actually gives the older folks the creeps. Thanks… 🙂 I’ve been living in the same city for 14 years now… and the climate 10+ years ago was never this hot here in summer. I remember thinking the climate was quite temperate here… was… ``` I do hope Bush will be kindly remembered like Chamberlain... as someone totally blind to the obvious disaster in the making. "There is no Global Warming in our times..." ``` ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [October 25, 2004, 3:24pm UTC](https://boards.straightdope.com/t/global-warming/270062/62 "2004-10-25T15:24:08Z")
> [@Sam Stone](#): > > The problem with that analysis is that you just pulled those numbers out of the air. You can show anything that way. > > Your equation assumes that we can maintain a constant annual increase in conservation. But that doesn’t seem likely to me, because we will very quickly run into the law of diminishing returns. Once we get past the ‘easy’ measures like turning the heat down a few degrees and remembering to turn our PC’s off at night, it starts to get harder. More fuel efficient cars? Great, except that it takes a long time for those cars to displace the existing fleet - a couple of decades. And if you force those cars on people when they aren’t willing to drive them, they won’t buy them. So then you’re left with putting taxes on energy to regulate consumption, and that is very expensive for the economy. Well your assumption of a flat 10% reduction is equally ad hoc. What I was really trying to get across is that conservation can make a significant impact on energy policy and to reject that out of hand is irresponsible. If you look you’ll see that the 2% reduction in use is tied to the energy used 2 years prior. Any newly developed energy consumer is likely to be made more efficient over time correct? Well I’ve modeled that as 2%. Since my model only speak to a 15 year period, not 100 years, a 2% increase in efficiency over 15 years doesn’t have enough time to run off into too many errors. Roughly speaking a product at the start of the period would have to reduce it consumption by a third by the end of the model. That is hardly wildly out of line and in the case of Canadian electrical consumption can save 54 billion dollars within the context of my numbers. Change the numbers to a 1% conservation factor and a 1.5% growth in electrical consumption and you wind up with an 8% increase compared to 23% increase. The economy still reaps a total of 25 billion dollars in savings, not counting the cost associated with building electrical plants etc. It comes down to reducing the number of required plants and so being able to build the least intrusive kind. > [@Sam Stone](#): > > And even if you do all that, all you do is push the problem down the road a few years. > > The only way to solve this problem is to find a different source of energy, and/or learn to sequester our carbon. We have to get the level of CO2 emissions down below the level of the Earth’s moderation forces to absorb it. Once we reach that ‘safe’ level (which is NOT 0 emissions), we can still use our fossil fuels, but as a much smaller source of energy. Remote turbines, that sort of thing. Energy consumption seems to be exponential, making small changes immediately allows for greater time to adjust. Time to better perfect C0[sub]2[/sub] sequestering, nuclear plant installation, investigate the C0[sub]2[/sub] holding capacity of the oceans etc… ---
**Author:** ![Steel\_Rat](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@Steel\_Rat](https://boards.straightdope.com/u/Steel_Rat)\ **Post date:** [November 5, 2004, 5:45pm UTC](https://boards.straightdope.com/t/global-warming/270062/63 "2004-11-05T17:45:25Z")
> [@jshore](#): > > …snip… > > In fact, it is understood that the warming from glacial to interglacial is initially triggered by increases in solar radiation due to oscillations in the earth’s orbit. However, for reasons that are not completely understood, this “trigger” then seems to lead to an increase in the CO2 levels, which in turn leads to more warming. The evidence from this is what tells us that the climate system is quite unstable and also gives us some estimate of the sensitivity of the climate to changes in CO2 levels (modulo the issue of how much of the warming in going from glacial to interglacial is due to the CO2 rise and how much is due to the other effects). Actually the vast majority (more than 80%, at a guess) of the ice core data that I have seen shows the opposite, that temperature rises **before** greenhouse gases. The problem is that most of this data is presented in a high-level view, where all you see is CO2 and Temp rising at the same time. If you get granular you see that simply isn’t the case. In some cases greenhouse gases rose significantly and temp dropped. In other cases the opposite occurred (greenhouse gases dropped and temp rose). Sometimes the time difference was hundreds of years, sometimes thousands. But the change was almost always abrupt. SR ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [November 5, 2004, 10:36pm UTC](https://boards.straightdope.com/t/global-warming/270062/64 "2004-11-05T22:36:10Z")
> [@Steel Rat](#): > > Actually the vast majority (more than 80%, at a guess) of the ice core data that I have seen shows the opposite, that temperature rises **before** greenhouse gases. The problem is that most of this data is presented in a high-level view, where all you see is CO2 and Temp rising at the same time. If you get granular you see that simply isn’t the case. In some cases greenhouse gases rose significantly and temp dropped. In other cases the opposite occurred (greenhouse gases dropped and temp rose). Sometimes the time difference was hundreds of years, sometimes thousands. But the change was almost always abrupt. The opposite of what? I said that the initial trigger is the orbital oscillations that lead to warming that lead to the release of greenhouse gases that lead to more warming. This is in fact compatible with the idea that the warming **starts** before the release of greenhouse gases (although it would imply that a lot of the warming occurs after the release of greenhouse gases). By the way, I believe that there are issues with the exact aligning of the temperature and CO2 data so you may be believing you can differentiate which came first beyond the extent to which the data warrants. There are a few good articles by the people who actually analyzed the ice core data. I’ll try to dig them up when I get the chance. ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [November 5, 2004, 10:45pm UTC](https://boards.straightdope.com/t/global-warming/270062/65 "2004-11-05T22:45:06Z")
For example, from [here](http://www.daviesand.com/Choices/Precautionary_Planning/New_Data/): > [@](#): > > The main significance of the new data lies in the high correlation between GTG concentrations and temperature variations over 420,000 years and through four glacial cycles. However, because of the difficulty in precisely dating the air and water (ice) samples, it is still unknown whether GTG concentration increases precede and cause temperature increases, or vice versa–or whether they increase synchronously. It’s also unknown how much of the historical temperature changes have been due to GTGs, and how much has been due to orbital forcing, ie, increases in solar radiation, or perhaps long-term shifts in ocean circulation. > > Whether the ultimate cause of temperature increase is excess CO2, or a different orbit, or some other factor probably doesn’t matter much. It could have been one or the other, or different combinations of factors at different times in the past. The effect is still the same. Nevertheless, the scientific consensus is that GTGs account for at least half of temperature increases, and that they strongly amplify the effects of small increases in solar radiation due to orbital forcing. ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [November 5, 2004, 10:49pm UTC](https://boards.straightdope.com/t/global-warming/270062/66 "2004-11-05T22:49:21Z")
And, here is what the [IPCC report](http://www.grida.no/climate/ipcc_tar/wg1/108.htm#334) says: > [@](#): > > The Vostok record of atmospheric CO2 and Antarctic climate is consistent with a view of the climate system in which CO2 concentration changes amplify orbitally-induced climate changes on glacial/inter-glacial time-scales (Shackleton, 2000). Changes during the present inter-glacial (until the start of the anthropogenic CO2 rise) have been small by comparison. Although complete explanations for these changes in the past are lacking, high-resolution ice core records establish that the human-induced increase of atmospheric CO2 over the past century is at least an order of magnitude faster than has occurred during the preceeding 20,000 years. ---
**Author:** ![Steel\_Rat](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@Steel\_Rat](https://boards.straightdope.com/u/Steel_Rat)\ **Post date:** [November 9, 2004, 8:58pm UTC](https://boards.straightdope.com/t/global-warming/270062/67 "2004-11-09T20:58:45Z")
> [@jshore](#): > > The opposite of what? I said that the initial trigger is the orbital oscillations that lead to warming that lead to the release of greenhouse gases that lead to more warming. This is in fact compatible with the idea that the warming **starts** before the release of greenhouse gases (although it would imply that a lot of the warming occurs after the release of greenhouse gases). > > By the way, I believe that there are issues with the exact aligning of the temperature and CO2 data so you may be believing you can differentiate which came first beyond the extent to which the data warrants. There are a few good articles by the people who actually analyzed the ice core data. I’ll try to dig them up when I get the chance. The opposite of the implication that CO2 and other greenhouse gases trigger any warming at all. The warming was already occurring, most likely due to solar variations and orbital oscillations, as you mentioned, how can it be said with any certainty that any continued warming is triggered by increases in greenhouse gases? Your subsequent quotes are reducng the time span significantly. 20,000 years is still a very small period of time. Even 420,000 is a small point in the scale. The fact remains that warming on the scale that we may be currently seeing HAS occurred in the ancient past. Let’s say that we significantly reduce the use of fossil fuels, I’m all for that, if for no other reason that to get out from under the middle eastern thumb of oppression. Will it really significantly reduce the rate at which atmospheric CO2 increases or decreases? How about all the breathing living things on the planet? They’re increasing at an exponential rate as well. why not just get rid of more humans, then they won’t breathe OR drive cars. SR ---
**Author:** ![Steel\_Rat](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@Steel\_Rat](https://boards.straightdope.com/u/Steel_Rat)\ **Post date:** [November 9, 2004, 9:11pm UTC](https://boards.straightdope.com/t/global-warming/270062/68 "2004-11-09T21:11:50Z")
> [@ralph124c](#): > > Some biologists ahve postulated that increased levels of CO2 might actually stimulate the growth of green plants…so much so that the extra CO2 would be absolrbed. That experiemental dome in Arizona: didn’t they study the effect of increasing CO2 levels? What happened there? I also wonder that if global warming is a real effect, then large areas of the arctic should begin to support plant life. This increase in biomass should absorb quite a bit of CO2 as well. Well, I mean plants DO use CO2 as a primary food source, and sunlight to synthesize it. So it’s pretty much an established fact. Plant nuseries sometimes use CO2 generators to promote plant growth. And it’s also why people believe talking to plants helps them grow. It’s not the talking, per se, but the burst of CO2 from the mouth of the speaker. So, we could all strap flower boxes to the backs of our cars and the CO2 will go right into the plants! See ya, gotta make a run down to the patent office 😉 SR ---
**Author:** ![legion](https://avatars.discourse-cdn.com/v4/letter/l/838e76/32.png) [@legion](https://boards.straightdope.com/u/legion)\ **Post date:** [November 10, 2004, 12:20am UTC](https://boards.straightdope.com/t/global-warming/270062/69 "2004-11-10T00:20:02Z")
> [@spingears](#): > > Global warming or…what was it Carl Sagan hapred on for years? Something about a feeze? > [@AndrewT](#): > > I think you are referring to Nuclear Winter, which is nothing to do with the subject at hand. I’m not so sure. I read somewhere of a theory that says global warming could lead to more ocean evaporation which could lead to greater cloud cover which could led more sunlight being reflected back into space which could lead to lower temperatures worldwide. ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [November 10, 2004, 1:37am UTC](https://boards.straightdope.com/t/global-warming/270062/70 "2004-11-10T01:37:57Z")
> [@Steel Rat](#): > > The opposite of the implication that CO2 and other greenhouse gases trigger any warming at all. The warming was already occurring, most likely due to solar variations and orbital oscillations, as you mentioned, how can it be said with any certainty that any continued warming is triggered by increases in greenhouse gases? Well, it depends what you mean by “any certainty”. If you really mean with “absolute certainty” then, no, we can’t be sure because science is not deductive but inductive and all knowledge is technically tentative. But, if you mean, what is the evidence that the CO2 and other greenhouse gases account for much of the warming, I’ll give you what I know of the evidence (with the caveat that a climate scientist could probably tell you more): (1) The idea that these gases should cause warming follows from very basic chemistry and physics. I.e., it is in their very nature to absorb infrared radiation such as that which the earth is re-radiating back into space. Admittedly, how this effect then gets magnified or reduced by various feedback mechanisms is still the subject of debate. (2) Best estimates of the amount of warming that should have occurred if the greenhouse gas increases were a major factor in the warming are in the right ballpark. (3) Estimates of the temperature rise that should occur due to the known variations in sunlight hitting the earth due to the orbital variations are too small to account for the warming that was seen. There have been attempts to propose amplifying mechanisms (other than through the increase in greenhouse gas concentrations) or other mechanisms for how changes in solar intensity or sunspot activity or whatnot could lead to sufficient warming alone but these have not panned out. > [@](#): > > Your subsequent quotes are reducng the time span significantly. 20,000 years is still a very small period of time. Even 420,000 is a small point in the scale. The fact remains that warming on the scale that we may be currently seeing HAS occurred in the ancient past. I’m not exactly sure what you are trying to say here. Are you seriously trying to argue that we need to understand every last detail about climatic variations over the last 4.5 billion years in order to be able to have some confidence about what might happen in the next few hundred years? These are the sorts of times when naysayers on anthropogenic climate change begin to sound a lot like creationists in the way they attack the science and say, “But, noone was around to see what really happened” and so forth. There is, by the way, evidence going back much further than 420,000 years (and some ice core data now goes back over 700,000 years I believe), but that data is much less detailed and much more sporadic than the ice core data. > [@](#): > > Let’s say that we significantly reduce the use of fossil fuels, I’m all for that, if for no other reason that to get out from under the middle eastern thumb of oppression. Will it really significantly reduce the rate at which atmospheric CO2 increases or decreases? How about all the breathing living things on the planet? They’re increasing at an exponential rate as well. why not just get rid of more humans, then they won’t breathe OR drive cars. You seem to be claiming that the CO2 increases might not be due to burning of fossil fuels. This is a view that you will find no support for in the scientific community, even among those who are naysayers on anthropogenic climate change. There may still be some uncertainties in the carbon cycle, but the basic evidence that fossil fuel emissions are leading to the rise in CO2 levels in not one of them. (Actually, the rise in CO2 levels has been such that thus far about 1/2 of the fossil fuel emissions are being uptaked by the biosphere and the hydrosphere…So, CO2 in the atmosphere is rising at about 1/2 the rate it would if there was no ability of the biosphere and hydrosphere to respond to these increases. However, at some point there is expected to be some saturation of the ability to re-uptake this CO2…And, perhaps, even some release of CO2 into the atmosphere, like happened during previous warming event.) As for human respiration, first off, the amount of CO2 that a human emits is pretty small compared to that of a car or other machine that runs on fossil fuels. Secondly (and see the discussion of your next point too), the thing about fossil fuels is that we are releasing a source of carbon that has long been locked away. Some of the other things that we do are just recycling carbon that has been transitioning back and forth between the atmosphere and organic material on shorter time scales. > [@](#): > > Well, I mean plants DO use CO2 as a primary food source, and sunlight to synthesize it. So it’s pretty much an established fact. Plant nuseries sometimes use CO2 generators to promote plant growth. And it’s also why people believe talking to plants helps them grow. It’s not the talking, per se, but the burst of CO2 from the mouth of the speaker. > > So, we could all strap flower boxes to the backs of our cars and the CO2 will go right into the plants! Land use policies can in fact have an effect on uptake of CO2, which is why the destruction of the tropical rainforest for example is a contributor to the rise in CO2 and why reforestation practices can help to some degree. Unfortunately, the amount of compensation that can be done this way is somewhat limited because plants just store carbon…They re-release it into the atmosphere when they die and decay. ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [November 10, 2004, 1:52am UTC](https://boards.straightdope.com/t/global-warming/270062/71 "2004-11-10T01:52:12Z")
> [@legion](#): > > I’m not so sure. I read somewhere of a theory that says global warming could lead to more ocean evaporation which could lead to greater cloud cover which could led more sunlight being reflected back into space which could lead to lower temperatures worldwide. Well, you are talking about a feedback effect. I.e., that warming would lead to a negative feedback through the mechanism you mention. This would not lead to net cooling but would lead to a stabilizing effect that would reduce the amount of warming that would occur. The biggest proponent of this idea is Richard Lindzen who has something called the “iris” effect whereby the earth’s climate is stabilized by this effect of warming leading to more clouds that lead to more sunlight being reflected back. However, most scientists don’t buy into this being a very important effect for a number of reasons: (1) It tends to predict a climate system that ought to be a lot more stable than what has historically been seen with the glaciation-deglaciation cycles and so forth. (2) The effects of clouds are quite complicated and depend on their geographic location, their height, the size of the water droplets in them and so forth. Intuitively, one can see this by realizing that clouds can act as a blanket too, reflecting back heat radiated from the earth…This is why in the winter, the coldest nights tend to be those with clear skies. At any rate, Lindzen made some specific statements about cloud cover in the tropics that he showed some data to support but subsequent studies have not tended to bear out his theory. (3) It is important to note that while the net feedback effect of clouds remains controversial, what is better understood is that the increase in uncondensed water vapor in the atmosphere due to the increased evaporation due to warming is a positive feedback effect because water vapor is, in a certain sense, a greenhouse gas. In fact, it is quite a potent one. [It is important to recognize that while water is a greenhouse gas in this sense, it is not one that it is easy for us to directly effect very much…i.e., unlike CO2, it doesn’t have a long residence time in the atmosphere so we don’t need to be too concerned about our direct emissions of water. The way we can affect its concentration in the atmosphere is through this indirect effect of putting long-lived greenhouse gases like CO2 into the atmosphere, causing warming, which then increases the equilibrium amount of water vapor in the atmosphere.] And, by the way, the talk of nuclear winter involved all the particulate matter kicked up which is a different issue and goes back to the known fact that large volcanic eruptions does tend to lead to cooling on the scale of months to a few years because of the particulate matter that can block solar radiation. ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [November 10, 2004, 2:10am UTC](https://boards.straightdope.com/t/global-warming/270062/72 "2004-11-10T02:10:38Z")
By the way, in regards to what scientists think the evidence from the past says about future climate, and particularly, the climate system’s sensitivity to CO2 concentration, [here](http://www.sciencemag.org/cgi/content/summary/306/5697/821) is the summary of a very recent article that appeared in _Science_. (I think everyone can get access to the summary, at least with free registration but you likely have to have a AAAS membership, or find the journal in the library in hardcopy form, to read the full article.) These scientists argue that the evidence from paleoclimate over millions of years suggests that the sensitivity of the climate to CO2 concentration is likely on the high end of what the climate models indicate: From the summary: > [@](#): > > Climate models and efforts to explain global temperature changes over the past century suggest that the average global temperature will rise by between 1.5º and 4.5ºC if the atmospheric CO2 concentration doubles. In their Perspective, Schrag and Alley look at records of past climate change, from the last ice age to millions of years ago, to determine whether this climate sensitivity is realistic. They conclude that the climate system is very sensitive to small perturbations and that the climate sensitivity may be even higher than suggested by models. From the article itself: > [@](#): > > Likewise, warm episodes in Earth’s history reveal a similar cautionary lesson. During the Eocene, 50 million years ago, palm trees grew in Wyoming (8) and deep ocean temperatures were more than 10ºC warmer than present (9). Because we do not know exactly how high the atmospheric CO2 concentration was at that time, we cannot use it as a direct measure of climate sensitivity. However, the extreme warmth at high latitudes–especially during the winter in continental interiors–cannot be simulated by climate models purely through elevating greenhouse gas concentrations (10). Special cloud feedbacks must be included that are not present in the models used to predict future climate change (10, 11). This observation suggests that feedbacks may be missing from current models and that future climate change may be underestimated in these models, particularly at high latitudes. > > … > > It would be a grave mistake to take these lessons from ancient climates as a reason to disregard the projections from climate models. The models are not perfect, but they represent the best understanding of the climate system from a century of observations and remain an essential tool for exploring future climate scenarios. Yet it is not surprising that there are some gaps in this understanding, because our atmosphere is heading toward a state far beyond the boundaries of all modern observations and calibrations. > > Paleoclimate studies help to fill these gaps. The lessons are surprisingly consistent, whether from warm climates or cold, whether from millions or thousands of years ago: The climate system is very sensitive to small perturbations. The release of greenhouse gases through human activities represents a large perturbation, sending our atmosphere to a state unlike any seen for millions of years. It behooves us to remember the past as we anticipate the future. ---
**Author:** ![dotchan](https://avatars.discourse-cdn.com/v4/letter/d/9d8465/32.png) [@dotchan](https://boards.straightdope.com/u/dotchan)\ **Post date:** [November 10, 2004, 3:21am UTC](https://boards.straightdope.com/t/global-warming/270062/73 "2004-11-10T03:21:52Z")
Of course, in the _really_ long term we’re headed for the heat death of the universe, but I doubt there’ll be any of us around to worry about it. Change hurts. But we need to do it. Not for the sake of change itself, but obviously we have been chopping up trees and burning stuff willy nilly and we can’t expect that to have no consequences whatsoever. And of course the US gets a giant bullseye on its back because we’ve sold ourselves the idea of a lifestyle that is completely unrealistic, both from an economic and environmental viewpoint, and we’re so unapologetic about it. We can’t stop consuming goods tomorrow, but we can try not to buy large, gas-guzzling cars to show off our manhood, curtail urban sprawl so we don’t destroy what greenery we’ve got left, and be a little nicer to our neighbors while we’re at it. …of course, the chances of that happening has about a snowball’s chance in hell, and I hear their heat index has hit historical highs… ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [November 10, 2004, 3:59am UTC](https://boards.straightdope.com/t/global-warming/270062/74 "2004-11-10T03:59:14Z")
Here, from the Technical Summary of the IPCC Third Assessment Report (TAR) on “The Scientific Basis” is some more info on CO2: > [@](#): > > The atmospheric concentration of CO2 has increased from 280 ppm in 1750 to 367 ppm in 1999 (31%, Table 1). Today’s CO2 concentration has not been exceeded during the past 420,000 years and likely not during the past 20 million years. The rate of increase over the past century is unprecedented, at least during the past 20,000 years (Figure 10). The CO2 isotopic composition and the observed decrease in Oxygen (O2) demonstrates that the observed increase in CO2 is predominately due to the oxidation of organic carbon by fossil-fuel combustion and deforestation. An expanding set of palaeo-atmospheric data from air trapped in ice over hundreds of millennia provide a context for the increase in CO2 concentrations during the Industrial Era (Figure 10). Compared to the relatively stable CO2 concentrations (280 ± 10 ppm) of the preceding several thousand years, the increase during the Industrial Era is dramatic. The average rate of increase since 1980 is 0.4%/yr. The increase is a consequence of CO2 emissions. Most of the emissions during the past 20 years are due to fossil fuel burning, the > rest (10 to 30%) is predominantly due to land-use change,especially deforestation. [Previous page](https://boards.straightdope.com/t/global-warming/270062.md?page=3)