Experts
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Physics Professor, IPCC Lead Author
Agree
There's little doubt that humans are largely responsible for the warming that has occurred over the last few decades. And even more important, there's a certainty that if the greenhouse gases build up at current rates, that the Earth will warm over the century to levels that haven't been seen in a million years. Over the past ten years or so, so-called skeptics have raised a number of objections, but these have been knocked down by research scientists...
Physics Professor, IPCC Lead Author
Agree
I'm acting as a reviewer for the latest last little bit of the IPCC reports, and you actually do get to see this vast body of evidence in appallingly large detail (and massive amounts of trees have gone into it) and that's what you can't explain away. So it tends to be people who focus on one very tiny aspect and say there could be other causes, but when you look at the evidence as a whole or even a large part of it, then I don't think there's anything in these [skeptical] arguments at all.
(IPCC) Scientific Body formed by U.N.
Mostly Agree
Most of the global average warming over the past 50 years is very likely due to anthropogenic GHG increases and it is likely that there is a discernible human-induced warming averaged over each continent (except Antarctica).
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Physicist, Environmentalist, Writer
Agree
The science isn't settled -- it's unsettling, and getting more so every year as the scientific community learns more about the catastrophic consequences of uncontrolled greenhouse gas emissions. The big difference I have with the doubters is they believe the IPCC reports seriously overstate the impact of human emissions on the climate, whereas the actual observed climate data clearly show the reports dramatically understate the impact.
US Energy Secretary, Nobel Laureate in Physics
Mostly Agree
There are stronger and stronger indications that global warming is happening, that it's caused by humans, and its consequences are looking more and more ominous. You can draw a parallel to the early days of [research into] cigarette smoking, the '50s and '60s, where scientists said, "Hey, there seems to be a link between lung cancer and cigarette smoking."
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Botanist, Writer, Nature Documentarian
Agree
I'm no longer sceptical. Now I do not have any doubt at all. I think climate change is the major challenge facing the world. I have waited until the proof was conclusive that it was humanity changing the climate. The thing that really convinced me was the graphs connecting the increase of carbon dioxide in the environment and the rise in temperature, with the growth of human population and industrialisation.
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United States President
Agree
There may still be disputes about exactly how much we're contributing to the warming of the earth's atmosphere and how much is naturally occurring, but what we can be scientifically certain of is that our continued use of fossil fuels is pushing us to a point of no return.
US Secretary of State 2009-, Democrat
Agree
At the top of the world [the Arctic], you hear stories -- affirmed by decades of scientific investigation [on anthropogenic global warming] -- of changing weather patterns, melting ice, retreating glaciers, unprecedented wildfires, eroding coasts, and invasive species. You can see the evidence with your own eyes. There are no climate change skeptics inside the Arctic Circle.
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U.S. Senator, Republican
Agree
The world is already feeling the powerful effects of global warming, and far more dire consequences are predicted if we let the growing deluge of greenhouse gas emissions continue...
Environmentalist, Former U.S. Vice President
Agree
We face a true planetary emergency. The climate crisis is not a political issue, it is a moral and spiritual challenge to all of humanity.
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Neutral
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Climatology Professor, Former IPCC Lead Author
Neutral
Atmospheric carbon dioxide continues to increase due to the undisputed benefits that carbon-based energy brings to humanity. This increase will have some climate impact through CO2's radiation properties. However, fundamental knowledge is meagre here, and our own research indicates that alarming changes in the key observations are not occurring.
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Disagree
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Meteorologist
Mostly Disagree
I predict that in the coming years, there will be a growing realization among the global warming research community that most of the climate change we have observed is natural, and that mankind’s role is relatively minor.
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Head of NIPCC, Astrophysics Professor
Mostly Disagree
The gap between the satellite observations and existing theory is large enough to cast serious doubt on all computer-model predictions of future warming. Whatever the cause of the gap, we cannot rely on GCM (General Circulation Models) forecasts of future warming. (GCMs are not even consistent with each other; their temperature forecasts vary by some 300 percent.) Until GCMs become validated by actual climate observations, they should not be used as the basis for policy.
Particle Physicist
Mostly Disagree
[Sun and cosmic rays] will probably be able to account for somewhere between a half and the whole of the increase in the Earth's temperature that we have seen in the last century.
Physics Professor
Disagree
The atmospheric greenhouse effect is a well known natural phenomenon, mostly caused by atmospheric water vapour, that keeps our planet warm and habitable whereas (anthropogenic = human-made) global warming refers to a small extra greenhouse warming (0.5-1 C/33 C; 1-5 %) allegedly arising from an increase in atmospheric concentration of the minority greenhouse effect gas CO2 (carbon dioxide) – the later increase in turn possibly arising from fossil fuel burning.
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Astronomer
Mostly Disagree
By the mid-21st century the planet will face another Little Ice Age, similar to the Maunder Minimum, because the amount of solar radiation hitting the Earth has been constantly decreasing since the 1990s and will reach its minimum approximately in 2041.
Botanist, Documentarian
Disagree
The link between the burning of fossil fuels and global warming is a myth. It is time the world's leaders, their scientific advisers and many environmental pressure groups woke up to the fact.
Geologist
Disagree
Personal beliefs on climate change and rising sea levels should be delayed until just one of the many predictions made since 1985 on the basis of carbon additions to the atmosphere comes true.
Marine Geophysical Professor
Disagree
With the complete discrediting of the ‘hockey stick’ curve of recent temperature change (McIntyre and McKitrick, 2003, 2005; Wegman, Scott and Said, 2006) that was the icon of their report, the IPCC case for dangerous human-caused warming now rests only on ambiguous anecdotal evidence, unvalidated computer models and misleading attribution studies (IPCC, 2007).
Geology Professor
Disagree
Most leading geologists, throughout the world, know that the IPCC's view of Earth processes are implausible if not impossible.
Geologist, President of the Geological Society of India
Disagree
The causes of these changes are cosmogenic...
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Mining Engineer
Mostly Disagree
So far the signal of a discernible human contribution to global climate change has not emerged from this natural variability or background noise.
Petition
Disagree
There are no experimental data to support the hypothesis that increases in human hydrocarbon use or in atmospheric carbon dioxide and other greenhouse gases are causing or can be expected to cause unfavorable changes in global temperatures, weather, or landscape... ...We also need not worry about environmental calamities even if the current natural warming trend continues. The Earth has been much warmer during the past 3,000 years without catastrophic effects.
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Governor of Alaska (Republican)
Disagree
A changing environment will affect Alaska more than any other state, because of our location. I'm not one though who would attribute it to being man-made.
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Ambiguous or Flip-Flop
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Popular Magazine
Agree
Be worried. Be very worried. ...Pump enough CO2 into the sky, and that last part per million of greenhouse gas behaves like the 212th degree Fahrenheit that turns a pot of hot water into a plume of billowing steam.
Popular Magazine
Disagree
Whatever the cause of the cooling trend, its effects could be extremely serious, if not catastrophic. Scientists figure that only a 1% decrease in the amount of sunlight hitting the earth's surface could tip the climatic balance, and cool the planet enough to send it sliding down the road to another ice age within only a few hundred years.
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Arguments
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If you
disagree, then you
necessarily
disagree with:
Is global warming caused primarily by humans?
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In 1896 Svante Arrhenius modeled the greenhouse effect, where gases in the atmosphere such as CO2 trap sunlight much like glass traps heat in a greenhouse. His principle is foundational in climatology, though today we have a more refined understanding of physical chemistry and we use Global Climate Models to predict that an increase in CO2 will actually result in global warming.
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It is very likely that glacial-interglacial CO2 variations have strongly amplified climate variations, but it is unlikely that CO2 variations have triggered the end of
glacial periods. Antarctic temperature started to rise several centuries before atmospheric CO2 during past glacial terminations.
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CO2 increases may accompany temperature increases rather than causing them. Indeed, some high resolution studies have suggested that the temperature increases precede the CO2 increases. Interestingly, also, ice core data shows strong temporal correlations between inferred temp. and amount of dust preserved in the ice core. Finally, the older geological record shows several dramatic examples of where CO2 concentration and global average temperature were either unrelated or even anti-correlated.
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If you
agree, then you
possibly
disagree with:
Is global warming caused primarily by humans?
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The intensity of the Sun is one of many input parameters used in climate models. None of the models used by the IPCC are able to successfully reproduce recent global temperature changes as a function of solar activity without also factoring in human greenhouse emissions. Some skeptics have suggested that this may be because of unknown complex feedbacks in Earth's climate.
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The TAR [Third Assessment Report] states that the changes in solar irradiance are not the major cause of the temperature changes in the second half of the 20th century unless those changes can induce unknown large feedbacks in the climate system.
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By the mid-21st century the planet will face another Little Ice Age, similar to the Maunder Minimum, because the amount of solar radiation hitting the Earth has been constantly decreasing since the 1990s and will reach its minimum approximately in 2041.
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If you
agree, then you
possibly
disagree with:
Is global warming caused primarily by humans?
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Oscillations in earth's orbit called Milankovitch cycles are at least partly responsible for climate change over tens and hundreds of thousands of years. However, the IPCC does not believe this is the cause of global warming over the last century.
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It is virtually certain that global temperatures during coming centuries will not be significantly influenced by a natural orbitally induced cooling. It is very unlikely that the Earth would naturally enter another ice age for at least 30 kyr.
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The accelerating warming of the Earth is not caused by man but by the regularities of the planets' circulation around the Sun.
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If you
agree, then you
possibly
disagree with:
Is global warming caused primarily by humans?
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Earth's atmosphere is bombarded by high energy particles from other galaxies called cosmic rays. An interesting theory is that when these particles hit Earth, they help form the type of clouds that reflect sunlight back into space, cooling the atmosphere. Since we know that the Sun forms a shield limiting the amount of cosmic radiation hitting the earth, the theory would imply that when the Sun is stronger, we'd have less cooling clouds, making the atmosphere hotter.
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I think that as a factor in climate change, it's pretty clear that we don't have any indication at this point that [cosmic rays] are important at all.
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[Sun and cosmic rays] will probably be able to account for somewhere between a half and the whole of the increase in the Earth's temperature that we have seen in the last century.
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If you
disagree, then you
possibly
disagree with:
Is global warming caused primarily by humans?
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The equilibrium of Earth's climate is a balancing act between the heating effect of the sun countered by the cooling effect of radiation from earth sent back into space. Earth's rich atmosphere and diverse surface complicates this equation with effects such as the greenhouse effect (the trapping of heat), giving rise to the study of climatology. The IPCC believes we understand this system well enough to predict it, at least in terms of global averages over decadal time periods.
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What the IPCC produces is not based on two years of literature, but 30 or 40 years of literature. We're not dealing with short-term weather changes, we're talking about major changes in our climate system. I refuse to accept that a few papers are in any way going to influence the long-term projections the IPCC has come up with.
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Our imperfect understanding of the causes and consequences of climate change means the science is far from settled.
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If you
agree, then you
necessarily
agree with:
Is global warming caused primarily by humans?
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The IPCC (Intergovernmental Panel on Climate Change) is a scientific body formed by the United Nations in 1988 to summarize research on climate change for the purpose of informing policy makers. Those who are skeptical of anthropogenic global warming have questioned the objectivity of the organization.
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The IPCC produces key scientific material that is of the highest relevance to policymaking, and is agreed word-by-word by all governments, from the most skeptical to the most confident. This difficult process is made possible by the tremendous strength of the underlying scientific and technical material included in the IPCC reports.
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The disappearance of the IPCC in disgrace is not only desirable but inevitable. The reason is, that the world will slowly realise that the "predictions" emanating from the IPCC will not happen. The absence of any "global warming" for the past eight years is just the beginning. Sooner or later all of us will come to realise that this organisation, and the thinking behind it, is phony. Unfortunately severe economic damage is likely to be done by its influence before that happens.
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Indirect Arguments
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If you
agree, then you
necessarily
agree with:
Are the causes of climate change well understood?
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Faith in any scientific theory is predicated on its predictive power. This makes validating climate models difficult: it may take years or even decades to conclusively match a model with observations. For this reason, both sides of the debate to some extent acknowledge that time will be the ultimate judge. However, many are already drawing conclusions from the IPCC's predictions made so far.
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We are not talking anymore about what climate models say might happen in the future. We are experiencing dangerous human disruption of the global climate and we're going to experience more.
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When Antarctica was cooling, some climate scientists said that was consistent with computer models for global warming. When a new study, such as Steig's, says it's warming, well that's just fine with the models, too. That's right: people glibly relate both warming and cooling of the frigid continent to human-induced climate change.
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If you
agree, then you
necessarily
agree with:
Are the causes of climate change well understood?
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The earth's climate is described with GCMs (General Circulation Models or Global Climate Models). GCMs are complex, containing many input variables and positive and negative feedback loops. These models are simulated on supercomputers to create predictions. The IPCC's predictions are based on an aggregate assessment of several GCMs.
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There is considerable confidence that climate models provide credible quantitative estimates of future climate change, particularly at continental scales and above. This confidence comes from the foundation of the models in accepted physical principles and from their ability to reproduce observed features of current climate and past climate changes. ... models have consistently provided a robust and unambiguous picture of significant climate warming in response to increasing greenhouse gases.
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There is of course much more wrong with state-of-the-art global circulation models (climate models) than the assumption and implementation of CO2-H2O feedback. Although these models are among the most elaborate predictive models of complex non-linear phenomena, they are nonetheless sweeping oversimplifications of the global climate system and its mechanistic intricacies.
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If you
agree, then you
necessarily
disagree with:
Does atmospheric CO2 cause significant global warming?
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The earth's climate is a system that contains feedback loops. If an input variable changes in a feedback loop, it effects the system in a way that changes the input variable itself. These changes cumulatively increase in a positive feedback loop, but progressively dampen in a negative feedback loop. The concern with increasing CO2, is that more CO2 in the atmosphere will warm the earth, in turn causing more CO2 to be released due to effects such as warmer oceans, i.e. a positive feedback loop.
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The small number of credible skeptics out there (e.g., Spencer, Lindzen) have spent much of the last decade searching for a negative feedback in our climate system. ... Most climate scientists, however, are reasonably certain that a negative feedback big enough to overwhelm the well-known positive feedbacks in the climate system [...] does not exist. ... it is extremely difficult to reconcile the existence of a big negative feedback with our past observations of climate variability.
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The real climate system appears to be dominated by “negative feedbacks” -- instead of the “positive feedbacks” which are displayed by all twenty computerized climate models utilized by the IPCC.
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If you
agree, then you
necessarily
agree with:
Is the IPCC objective?
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Many believers in Anthropogenic Global Warming claim that the scientific debate is over.
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There are no longer any serious scientists producing peer reviewed scientific journal articles that [deny anthropogenic global warming]. The real scientific debate is over. The people who say global warming isn't real, they must get together on Saturday nights and party with the ones who think the moon landing was staged on a movie lot in Arizona.
Al Gore
Environmentalist, Former U.S. Vice President
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Most leading geologists, throughout the world, know that the IPCC's view of Earth processes are implausible if not impossible.
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If you
agree, then you
possibly
disagree with:
Is the IPCC objective?
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Anthropogenic Global Warming has become a huge multinational concern, with many people's career and credibility dependent on its truth. As such, some skeptics claim that scientists now fear that challenging the new orthodoxy can result in a lack of funding. Believers have pointed the finger to the fossil fuel industry for spreading misinformation about the facts, and criticized politicians uneasy dealing with the economic impacts of climate change for stonewalling.
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Instead of recognizing the irrefutable evidence, this Administration has launched a war on science itself. Political appointees have censored studies on global warming, silenced climate experts. According to a survey by the Union of Concerned Scientists, nearly 3/4 of climate experts witnessed inappropriate interference in climate research.
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Many of my colleagues with whom I spoke share these views and report on their inability to publish their skepticism in the scientific or public media.
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Comments
Collective
Agree
This debate is choked with irrelevant arguments on both sides. What matters is how the science from the leading advocates on each side compare. The side who believes Global Warming is caused by humans is best represented by the IPCC, a group of scientists working for the United Nations. The opposition is probably best represented by Fred S. Singer, a respected astrophysicist who heads the NIPCC (Nongovernmental Panel for Climate Change). The IPCC's conclusions are heavily reliant on GCMs (Global Climate Models), which simulate Earth's past, current, and future climate on computers. The inputs for these models include natural fluctuations, such as variance in the Sun's radiation and Earth's orbit. Applied to the distant past, these climate models can even successfully reproduce the cycles of glacial / interglacials as functions of variances in Earth's orbit, called Milankovitch cycles. Applied to the last hundred years, climate models are unable to reproduce Earth's climate without taking into account the forcing effect of excess greenhouse gases in our atmosphere. Note that fringe skeptics make the absurd claim that CO2 and methane don't have a greenhouse effect, but they aren't taken seriously by even skeptical climatologists. The opposition, the NIPCC, believe the cause of recent climate change is very likely to be galactic cosmic radiation. This theory was a long shot before it was even tested, and has since been shot down in a peer reviewed paper, that the NIPCC intentionally ignores. The NIPCC also point out that climate is too complex to model. This is inconsistent with their claim that cosmic rays are very likely to be the main cause of climate change. They go further, saying that computer models cannot be used to model climate, but they don't prove it scientifically. A sufficient proof would be to demonstrate that small perturbations in the inputs to a model could yield radically different climates. There is sadly no academic rigor in their criticism of computer models. The skeptics' position is inconsistent and unsubstantiated. In contrast, the IPCC's position is consistent, and backed up by scientific evidence. The truth is clear.
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Edit (wiki edits require login)
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Disagree
The IPCC have yet to make convincing predictions. Karl Popper, a philosopher of science, was right to say that a scientific theory is predicated on its predictive power. What have the IPCC predicted so far that would have been difficult to guess? Even James Hansen, one of the world's leading climatologists, admits that the evidence so far has yet to validate the theory. When they guessed that the sea level would rise a few millimeters, it turned out they were wrong by 50%. Now, given the sea level fluctuates naturally in this range anyway, this prediction is far from impressive. Yet the media latched onto the fact that the sea level rose *more* than the IPCC said it did, as if this validated that the IPCC was right all along. Well actually, in science, what matters, is how accurate you are. Being off by 50% is shocking and doesn't prove the theory whatsoever. It shows that the real causes are not understood. There is just too much room for error in climate model predictions to base policy on them. If the IPCC was objective, they'd admit that.
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Individual
Agree
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gave their takeonit
on 06 May 2009
Agree
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gave their takeonit
on 05 May 2009
Mostly Agree
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Disagree
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gave their takeonit
on 27 Apr 2009
Mostly Disagree
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