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How We Know Global Warming is Real

Dr. Tapio Schneider discusses the science behind human-induced climate change. He is a climate scientist and Professor of Environmental Science and Engineering at the California Institute of Technology.

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The Science Behind Human-induced Climate Change

Atmospheric carbon dioxide concentrations are higher today than at any time in at least the past 650,000 years. They are about 35% higher than before the industrial revolution, and this increase is caused by human activities, primarily the burning of fossil fuels. Carbon dioxide is a greenhouse gas, as are methane, nitrous oxide, water vapor, and a host of other trace gases. They occur naturally in the atmosphere. Greenhouse gases act like a blanket for infrared radiation, retaining radiative energy near the surface that would otherwise escape directly to space. An increase in atmospheric concentrations of carbon dioxide and of other greenhouse gases augments the natural greenhouse effect; it increases the radiative energy available to Earth’s surface and to the lower atmosphere. Unless compensated for by other processes, the increase in radiative energy available to the surface and the lower atmosphere leads to warming. This we know. How do we know it?

figure 1

Figure 1. Carbon dioxide concentrations in Antarctica over 400,000 years. “The graph combines ice core data with recent samples of Antarctic air. The 100,000-year ice age cycle is clearly recognizable.” (Data sources: Petit et al. 1999; Keeling and Whorf 2004; GLOBALVIEW-CO2 2007.)

How do we know carbon dioxide concentrations have increased?

The concentrations of carbon dioxide and other greenhouse gases in atmospheric samples have been measured continuously since the late 1950s. Since then, carbon dioxide concentrations have increased steadily from about 315 parts per million (ppm, or molecules of carbon dioxide per million molecules of dry air) in the late 1950s to about 385 ppm now, with small spatial variations away from major sources of emissions. For the more distant past, we can measure atmospheric concentrations of greenhouse gases in bubbles of ancient air preserved in ice (e.g., in Greenland and Antarctica). Ice core records currently go back 650,000 years; over this period we know that carbon dioxide concentrations have never been higher than they are now. Before the industrial revolution, they were about 280 ppm, and they have varied naturally between about 180 ppm during ice ages and 300 ppm during warm periods (Fig. 1). Concentrations of methane and nitrous oxide have likewise increased since the industrial revolution (Fig. 2) and, for methane, are higher now than they have been in the 650,000 years before the industrial revolution.

figure 2

Figure 2. Greenhouses gases then and now.

How do we know the increase in carbon dioxide
concentrations is caused by human activities?

There are several lines of evidence. We know approximately how much carbon dioxide is emitted as a result of human activities. Adding up the human sources of carbon dioxide — primarily from fossil fuel burning, cement production, and land use changes (e.g., deforestation) — one finds that only about half the carbon dioxide emitted as a result of human activities has led to an increase in atmospheric concentrations. The other half of the emitted carbon dioxide has been taken up by oceans and the biosphere — where and how exactly is not completely understood: there is a “missing carbon sink.”

Human activities thus can account for the increase in carbon dioxide concentrations. Changes in the isotopic composition of carbon dioxide show that the carbon in the added carbon dioxide derives largely from plant materials, that is, from processes such as burning of biomass or fossil fuels, which are derived from fossil plant materials. Minute changes in the atmospheric concentration of oxygen show that the added carbon dioxide derives from burning of the plant materials. And concentrations of carbon dioxide in the ocean have increased along with the atmospheric concentrations, showing that the increase in atmospheric carbon dioxide concentrations cannot be a result of release from the oceans. All lines of evidence taken together make it unambiguous that the increase in atmospheric carbon dioxide concentrations is human induced and is primarily a result of fossil fuel burning. (Similar reasoning can be evoked for other greenhouse gases, but for some of those, such as methane and nitrous oxide, their sources are not as clear as those of carbon dioxide.)

How can such a minute amount of carbon dioxide
affect Earth’s radiative energy balance?

Concentrations of carbon dioxide are measured in parts per million, those of methane and nitrous oxide in parts per billion. These are trace constituents of the atmosphere. Together with water vapor, they account for less than 1% of the volume of the atmosphere. And yet they are crucially important for Earth’s climate.

Earth’s surface is heated by absorption of solar (shortwave) radiation; it emits infrared (longwave) radiation, which would escape almost directly to space if it were not for water vapor and the other greenhouse gases. Nitrogen and oxygen, which account for about 99% of the volume of the atmosphere, are essentially transparent to infrared radiation. But greenhouse gases absorb infrared radiation and re-emit it in all directions. Some of the infrared radiation that would otherwise directly escape to space is emitted back toward the surface. Without this natural greenhouse effect, primarily owing to water vapor and carbon dioxide, Earth’s mean surface temperature would be a freezing -1°F, instead of the habitable 59°F we currently enjoy. Despite their small amounts, then, the greenhouse gases strongly affect Earth’s temperature. Increasing their concentration augments the natural greenhouse effect.

figure 3

Figure 3. How We Know the Globe is Warming.

How do increases in greenhouse gas concentrations
lead to surface temperature increases?

Increasing the concentration of greenhouse gases increases the atmosphere’s “optical thickness” for infrared radiation, which means that more of the radiation that eventually does escape to space comes from higher levels in the atmosphere. The mean temperature at the level from which the infrared radiation effectively escapes to space (the emission level) is determined by the total amount of solar radiation absorbed by Earth. The same amount of energy Earth receives as solar radiation, in a steady state, must be returned as infrared radiation; the energy of radiation depends on the temperature at which it is emitted and thus determines the mean temperature at the emission level. For Earth, this temperature is -1°F — the mean temperature of the surface if the atmosphere would not absorb infrared radiation. Now, increasing greenhouse gas concentrations implies raising the emission level at which, in the mean, this temperature is attained. If the temperature decreases between the surface and this level and its rate of decrease with height does not change substantially, then the surface temperature must increase as the emission level is raised. This is the greenhouse effect. It is also the reason that clear summer nights in deserts, under a dry atmosphere, are colder than cloudy summer nights on the U.S. east coast, under a relatively moist atmosphere (Figs. 4 and 5).

figure 4 and 5

Figure 4 and 5. Two Cheers for the Greenhouse Effect. Some global warming is necessary in order to make the Earth habitable for creatures like us. These two graphics show how it works. The IPCC caption reads: “Estimate of the Earth’s annual and global mean energy balance. Over the long term, the amount of incoming solar radiation absorbed by the Earth and atmosphere is balanced by the Earth and atmosphere releasing the same amount of outgoing longwave radiation. About half of the incoming solar radiation is absorbed by the Earth’s surface. This energy is transferred to the atmosphere by warming the air in contact with the surface (thermals), by evapotranspiration and by longwave radiation that is absorbed by clouds and greenhouse gases. The atmosphere in turn radiates longwave energy back to Earth as well as out to space.” Source: Kiehl and Trenberth (1997). (Graphics are FAQ 1.1, 1.3, Figure 1 from the IPCC Report.)

In fact, Earth surface temperatures have increased by about 1.3°F over the past century (Fig. 3). The temperature increase has been particularly pronounced in the past 20 years (for an illustration, see the animations of temperature changes). The scientific consensus about the cause of the recent warming was summarized by the Intergovernmental Panel on Climate Change (IPCC) in 2007: “Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations… The observed widespread warming of the atmosphere and ocean, together with ice mass loss, support the conclusion that it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing, and very likely that it is not due to known natural causes alone.”

figure 6

Figure 6. The History of Climate Models. The IPCC caption reads: “The complexity of climate models has increased over the last few decades. The additional physics incorporated in the models are shown pictorially by the different features of the modelled world.” (Graphic is Figure 1.2 from the IPCC Report.)

The IPCC conclusions rely on climate simulations with computer models (Fig. 6). Based on spectroscopic measurements of the optical properties of greenhouse gases, we can calculate relatively accurately the impact increasing concentrations of greenhouse gases have on Earth’s radiative energy balance. For example, the radiative forcing owing to increases in the concentrations of carbon dioxide, methane, and nitrous oxide in the industrial era is about 2.3 Watts per square meter. (This is the change in radiative energy fluxes in the lower troposphere before temperatures have adjusted.) We need computer models to translate changes in the radiative energy balance into changes in temperature and other climate variables because feedbacks in the climate system render the climate response to changes in the atmospheric composition complex, and because other human emissions (smog) also affect climate in complex ways. For example, as the surface and lower atmosphere warm in response to increases in carbon dioxide concentrations, the atmospheric concentration of water vapor near the surface increases as well. That this has to happen is well established on the basis of the energy balance of the surface and relations between evaporation rates and the relative humidity of the atmosphere (it is not directly, as is sometimes stated, a consequence of higher evaporation rates).

Water vapor, however, is a greenhouse gas in itself, and so it amplifies the temperature response to increases in carbon dioxide concentrations and leads to greater surface warming than would occur in the absence of water vapor feedback. Other feedbacks that must be taken into account in simulating the climate response to changes in atmospheric composition involve, for example, changes in cloud cover, dynamical changes that affect the rate at which temperature decreases with height and hence affect the strength of the greenhouse effect, and surface changes (e.g., loss of sea ice). Current climate models, with Newton’s laws of motion and the laws of thermodynamics and radiative transfer at their core, take such processes into account. They are able to reproduce, for example, Earth’s seasonal cycle if all such processes are taken into account but not, for example, if water vapor feedback is neglected. The IPCC’s conclusion is based on the fact that these models can only match the observed climate record of the past 50 years if they take human-induced changes in atmospheric composition into account. They fail to match the observed record if they only model natural variability, which may include, for example, climate responses to fluctuations in solar radiation (Fig. 7).

figure 3

Figure 7. Global and Continental Temperature Change. The IPCC caption reads: “Comparison of observed continental — and global — scale changes in surface temperature with results simulated by climate models using either natural or both natural and anthropogenic forcings. Decadal averages of observations are shown for the period 1906–2005 (black line) plotted against the center of the decade and relative to the corresponding average for the period 1901–1950. Lines are dashed where spatial coverage is less than 50%. Darker shaded bands show the 5 to 95% range for 19 simulations from five climate models using only the natural forcings due to solar activity and volcanoes. Lighter shaded bands show the 5 to 95% range for 58 simulations from 14 climate models using both natural and anthropogenic forcings.” (Graphic is Figure SPM.4 from the IPCC Report.)

Climate feedbacks are the central source of scientific (as opposed to socio-economic) uncertainty in climate projections. The dominant source of uncertainty are cloud feedbacks, which are incompletely understood. The area covered by low stratus clouds may increase or decrease as the climate warms. Because stratus clouds are low, they do not have a strong greenhouse effect (the strength of the greenhouse effect depends on the temperature difference between the surface and the level from which infrared radiation is emitted, and this is small for low clouds); however, they reflect sunlight, and so exert a cooling effect on the surface, as anyone knows who has been near southern California’s coast on an overcast spring morning. If their area coverage increases as greenhouse gas concentrations increase, the surface temperature response will be muted; if their area coverage decreases, the surface temperature response will be amplified. It is currently unclear how these clouds respond to climate change, and climate models simulate widely varying responses. Other major uncertainties include the effects of aerosols (smog) on clouds and the radiative balance and, on timescales longer than a few decades, the response of ice sheets to changes in temperature.

Uncertainties notwithstanding, it is clear that increases in greenhouse gas concentrations, in the global mean, will lead to warming. Although climate models differ in the amount of warming they project, in its spatial distribution, and in other more detailed aspects of the climate response, all climate models that can reproduce observed characteristics such as the seasonal cycle project warming in response to the increases in greenhouse gas concentrations that are expected in the coming decades as a result of continued burning of fossil fuels and other human activities such as tropical deforestation. The projected consequences of the increased concentrations of greenhouse gases have been widely publicized. Global-mean surface temperatures are likely to increase by 2.0 to 11.5°F by the year 2100, with the uncertainty range reflecting scientific uncertainties (primarily about clouds) as well as socio-economic uncertainties (primarily about the rate of emission of greenhouse gases over the 21st century). Land areas are projected to warm faster than ocean areas. The risk of summer droughts in mid-continental regions is likely to increase. Sea level is projected to rise, both by thermal expansion of the warming oceans and by melting of land ice.

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Less widely publicized but important for policy considerations are projected very long-term climate changes, of which some already now are unavoidable. Even if we were able to keep the atmospheric greenhouse gas concentration fixed at its present level — this would require an immediate and unrealistically drastic reduction in emissions — the Earth surface would likely warm by another 0.9–2.5°F over the next centuries. The oceans with their large thermal and dynamic inertia provide a buffer that delays the response of the surface climate to changes in greenhouse gas concentrations. The oceans will continue to warm over about 500 years. Their waters will expand as they warm, causing sea level rise. Ice sheets are thought to respond over timescales of centuries, though this is challenged by recent data from Greenland and Antarctica, which show evidence of a more rapid, though possibly transient, response. Their full contribution to sea level rise will take centuries to manifest. Studies of climate change abatement policies typically end in the year 2100 and thus do not take into account that most of the sea level rise due to the emission of greenhouse gases in the next 100 years will occur decades and centuries later. Sea level is projected to rise 0.2–0.6 meters by the year 2100, primarily as a result of thermal expansion of the oceans; however, it may eventually reach values up to several meters higher than today when the disintegration of glaciers and ice sheets contributes more strongly to sea level rise. (A sea level rise of 4 meters would submerge much of southern Florida.)

Certainties and Uncertainties

While there are uncertainties in climate projections, it is important to realize that the climate projections are based on sound scientific principles, such as the laws of thermodynamics and radiative transfer, with measurements of optical properties of gases. The record of past climate changes that can be inferred, for example, with geochemical methods from ice cores and ocean sediment cores, provides tantalizing hints of large climate changes that occurred over Earth’s history, and it poses challenges to our understanding of climate (for example, there is no complete and commonly accepted explanation for the cycle of ice ages and warm periods). However, climate models are not empirical, based on correlations in such records, but incorporate our best understanding of the physical, chemical, and biological processes being modeled. Hence, evidence that temperature changes precede changes in carbon dioxide concentrations in some climate changes on the timescales of ice ages, for example, only shows that temperature changes can affect the atmospheric carbon dioxide concentrations, which in turn feed back on temperature changes. Such evidence does not invalidate the laws of thermodynamics and radiative transfer, or the conclusion that the increase in greenhouse gas concentrations in the past decades is human induced.

This article can be found in
Skeptic volume 14 number 1

volume 14 number 1
A Climate of Belief

How We Know Global Warming is Real: The Science Behind Human-induced Climate Change; How to solve the global warming problem by 2020…
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idgl
September 3, 2013 5:34 am

The articles references the Vostok ice core data (Petit et all, 1999) but fails to mention that for 420000 years air temperature and CO2 levels moved in step with the CO2 level lagging the temperature by 800 years. To say that increased CO2 levels cause a rise in temperature is akin to saying that lung cancer causes smoking.
As ocean temperatures rise dissolved CO2 is released and when the oceans cool CO2 is reabsorbed.

blurred lines
August 24, 2013 1:28 pm

I know you want it

Tim
August 9, 2013 4:46 am

Two things:
1. being a skeptic -means being reasonably skeptical – not ridiculously skeptical of everything. Eg. I know that smoking causes lung cancer, I have done no reading into this but it seems so completely accepted – why waste my time. I might as well try to prove that solid walls are not actually solid and can be walked through but I am also not skeptical of this.

2. A lot of the criticism seems to be on weather measurements, surely one can easily model the impact of extra carbon in the atmosphere in very controlled greenhouse conditions. And one can easily get carbon levels through ice core examples. So we know that humans have put extra carbon in the atmosphere. Extra carbon causes the earth to heat. If I drop a rock into a well – I know what will happen even though I can’t see it.

Marc Aurele
July 25, 2013 1:03 am

Nice models!
How is the fund raising going?

Slartibartfast
June 2, 2013 9:28 am

At least the faux skeptics protesting their disappoint have half a chance of convincing a few genuine skeptics, but most buffoons posting crud here are deluding themselves.

Slartibartfast
June 2, 2013 9:20 am

Trolls! A pox on all your mother’s basements!

poop
May 20, 2013 11:04 am

shut yer mouths u sicle cell havin cock goblins

xXx420xBlazeXitXfagetxXx
May 20, 2013 11:01 am

pickle bob shit stain u a lyin snake foh

pickle bob shit stain
May 20, 2013 11:00 am

take a look, nigga. in a book, mah nigga.

shelby bagans and courtney bieber
May 14, 2013 11:27 am

thank you for this article. we really enjoyed this thank you.

Cyberknight
May 13, 2013 11:05 am

This article never even talks about the very thing I was just looking for: proof!

I have been looking all over the web, and every article that is supposed to “convince” me that GHGs are causing global warming have completely failed. Every one of them, including this one, use “Post Hoc Ergo Propter Hoc” fallacies (after which therefore because of which). Yes, global average temperatures are increasing. Yes, GHGs are increasing. However, what proof do we have that temps are rising BECAUSE GHGs are rising? None at all!

This article does a very good job of telling how GHGs COULD POTENTIALLY cause warming, but if you want to convince a “skeptic”, you need better evidence.

rape a bitch
April 28, 2013 2:08 am

I think the article would be better if it provided examples of repeatable experiments that showed elevated CO2 and temperature are harmful to biodiversity, then framed the global warming controversy in terms of risk management to avoid damage to local biodiversity. The remote sensing temperature data available from the US government does not go back far enough to show any clear trend.

Slartibartfast
June 2, 2013 9:25 am
Reply to  rape a bitch

Your selected user name says enough.

poop
April 26, 2013 9:14 am

Niggers are ugly

Lol
April 24, 2013 1:42 pm

I am terribly sorry for my horrific behaviour i am very very sorry for my stupidity

Alex
April 24, 2013 6:21 am

“lol” you’re comments are most immature. Please stop posting silly comments in future.

lol
April 24, 2013 6:18 am

u load of jammy cunts

lol
April 24, 2013 6:16 am

lol, lol, lol, lol, lol.

Bob
February 3, 2013 3:00 am

are your graphs accurate?!

RS Amblee
January 10, 2013 1:52 pm

Global Warming is a case of mistaken identity!
Global warming should not have been called global warming at all.This misnomer has confused many, and has added to its development as such a controversial subject in the world today.

“If global warming exists, why is it so darn cold outside?”

You may have heard these kind of retorts quite often. Globally, the Earth has warmed about 2 degrees Celsius. This is number is really not very big,and should not raise our eyebrows. What we should really be talking about is the climactic effect this raise in temperature has rather than the warming itself. Many of us do not know how delicately our atmosphere is balanced. Wind speeds and rain patterns are heavily dependent on the global temperature gradient. Our easterly and westerly winds are so well set that we have a very well defined climate geography. Even if there is a slight change in the global temperature gradient, be it half a degree, it will affect global wind patterns which in turn affects rain patterns. This is why many places that used to receive regular rainfall are now suffering from drought, and many formerly dead-dry places are flooded. Colder regions are becoming milder and some hot regions are getting surprise snowfalls. It is hard to comprehend that all this abnormal weather behavior is because of a 2 degree temperature hike.

Global warming is not heating up our neighborhood. The localrise in temperature is because the disturbed wind pattern, which actually is caused by the 2 degree rise in global temperature, circulates warm air from hotter regions to colder regions and vice-versa where it did not used to before. To make it moreclear, if you see an unusual rise of 20 degrees in the winter, it is the side effect of disturbed weather patterns because of the 2 degree global temperature rise.

The orientation of forests and grass lands are fully dependent on global rain patterns. It is the stability of this system that keeps our ecosystems consistent, which is something that we all depend on. Anychange in rain patterns will have disastrous effects.

We are very dependent on mother nature, and this dependency will be heavily challenged in the days to come. Whether we believe in global warming or not, the underlying issue is that we should not be living under the mercy of a delicately balanced ecosystem. Throughout man’s history, Mother Nature has provided for us, and we had no other alternative but todepend on her. But now with all our technological developments, we have the tools necessary to break our umbilical cord with Mother Nature. However, it is not happening fast enough, and the reason for this is pureand simple – money. Anything that Mother Nature gives us is free (e.g.food, water,air,light).This has made us develop environmentally dependent technologies (irrigation, fresh water utilization) and stuck to this system. Now as the same ecosystem is changing, it is throwing us a challenge. Rain is not dependable any more. Fresh water supply is changing. The economics of food supply is being rewritten. Floods, hurricanes, and twisters are happening more frequently and are causing billions of dollars in damages. These challenge from global climate change are forcing us to move away from our dependency on the ecosystem and control our own world.

Even without man-made global warming, climate change would have been inevitable as our atmosphere is delicately balanced. The world climate has historically gone through a cyclic pattern of climate shifts and ice ages. It is a great relief that climate change is happening in this current age, when we are ready with technology. Surviving thru the ice age and preserving the human race is something our ancestors have proved is possible, but if it had happened just two hundred years ago, we would have lost all the marvels of human civilization and survived with only with the bare necessities. But now the scenario is different. It is just a matter of time before we integrate robotics and automation in our lives and evolve towards an advanced future. We have the technology to protect us,and free us from our dependency on nature.

– R.S. Amblee
Author “The Art of Looking Into the Future: The Five Principles of Technological Evolution”

Kyle Serrecchia
January 10, 2013 12:07 am

Even if this is all true, and it probably all is, this says nothing about whether or not it will be catastrophic and warrants any action to be taken whatsoever. THAT has not been proven. This seems to be attacking a strawman. I don’t know many people, even so called global warming denialists, who would disagree that warming is occurring and yet they still would be against any carbon emissions reductions because it hasn’t been proven global warming will be harmful. Or, even if it will in fact be harmful, that it will be more harmful than cutting industry would be. So even if it is proven someday that the warming that we are certain is occurring is going to be horrible, scientists would still need to confer with economists in order to ensure that the “cure” of cutting emissions and thus hurting the energy industry upon which all of our lives depend would not in fact be worse than the disease.

Slartibartfast
June 2, 2013 9:18 am

Another standard denier talking point, either the third or fourth goal post position as they keep getting moved.

Tris
November 22, 2012 3:54 pm

I learned more from the comments than the article. Thank you for helping me understand my world a little better.
here is what I learned
There is no solid evidence that c02 is linked to global warming
There is solid evidence that the the world is warming
there is solid evidence that there was a ice age and that man was existed during it.
There is solid evidence that many animals have gone extinct because of climate change and because of humans.
There is solid evidence we are hurting the environment.
There is solid evidence that there are too many humans for the environment to take.
There is solid evidence that there is not enough oil for everyone and we will run out.

The more I learn about the world confused and awed I get.

Henry Hopp
November 15, 2012 11:11 am

You know what I think we should do about global warming? Give ice cream to the whole world so that everybody cools down and thus, the world. :D

Slartibartfast
June 2, 2013 9:16 am
Reply to  Henry Hopp

You know why nobody cares what you think?

sick of stupidity
November 13, 2012 8:23 pm

Why is it that everyone is now a scientist and at that a MUCH MORE INTELLIGENT scientist than Mr. Schneider…who is an actual Professor at a prestigious university–Cal Tech. P.S. that means he has a degree, in fact two + cuz you cant teach this stuff if you dont have a Master’s. you all pick at what you want but ask yourself this: how can you convince yourself that the world’s most studied scientists (with degrees in REAL atmospheric, oceanographic, physical, chemical science and math) are secretly plotting against you. WHAT WOULD FUEL THEM TO LEAD YOU TO FALSE CLAIMS? what do they get out of faking this stuff? Then ask yourself this: why are oil companies and politicians involved with oil/natural gas/coal companies against it?what do THEY have to gain from denouncing climate change?

you guys are seriously stupid. stupid stupid stupid. luck for you! stupid can be educated! at least… that’s what they keep telling me…

bessy
November 7, 2012 11:50 am

this is to long.

Slartibartfast
June 2, 2013 9:15 am
Reply to  bessy

Your ‘to’ is too short.

Tesla
July 21, 2012 5:49 am

The temperature going up or down, the accuracy of the readings, or the manifestations of a change in temperature on this planet are all irrelevant to an extent.

Just because one thing happens and another thing happens at the same time does not mean they are necessarily related. So carbon goes up and temperatures go up. Linked or a coincidence? What gasses are going down at this time? Linked or coincidence.

Most of the ‘science’ and articles say ‘the increase in GHG’s is blah blah’ inferring that its a given that CO2 is responsible, but where is the evidence that GHG’s exist?
Where is the science that CO2 holds heat? How can it, it is an inert gas!!! It is a gas, essential to plants and provides an important function. Show me the science.

Most of the ‘science’ and articles say ‘the increase in GHG’s is blah blah’ but where is the evidence that GHG’s exist? Water vapour I can understand might hold heat, but this disburses rapidly.

Extrapolating a graph into the future is a guess, not absolute fact. If we extrapolate the worlds population 50 years into the future it might show we will have 100 billion people on the planet. This can’t possibly occur, so extrapolations are meaningless, or at least can’t be cited as ‘absolute truth’

I read somewhere (yes, its only heresy until its proved, but it might be worth checking) that the planet is at present colder than it has been for 83% of its recorded and ascertainable history. Food for thought.

The other danger in making carbon dioxide the bogeyman is that attention is taken off all the other chemical and gases that are polluting the planet, some of which may indeed be effecting the atmosphere.

I do agree, however, that we can’t keep shitting in our own nest and expect our children to have happy, healthy lives, so as a permaculturalist I work towards creating a cleaner planet by minimising my footprint. Not my carbon footprint necessarily but my energy, waste, resource footprint.

This experiment in capitalism, consumerism and fiat currencies is almost over. Bring it on I say. Only then can we rebuild using sustainable, ethical practices.

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