Few reputable scientists at this point dispute the claim that humanity has played some role in global warming. Nonetheless, the public opinion on this issue is somewhat fragile, with some disagreeing on the degree to which global warming might also be caused simply by natural changes in the earth’s climate. Some claim that humans are the chief cause of the warming that has occurred over roughly the past century, while others claim that our role has been relatively insignificant as compared to natural forces. Therefore, the debate roughly defined here centers on the question of whether human are the “chief” or “most significant” cause of the recent global warming trend seen over the past century and today. This debate is important in the way of determining policy responses. If, for instance, the human cause of global warming was concluded to be relatively minor, then some would argue that policies attempting to address these human causes (carbon emissions regulations…) are misplaced. Conversely, a conclusion that humans are the chief cause of global warming would provide valid support for efforts that attempt to stem these human-causes. Of course, conclusions that humans are, for instance, 30% of the cause would create a more challenging set of questions in the way of how to prioritize a human response. Still, the undeniable fact that the earth is getting warmer leads to a range of separate debates that need not consider the underlying cause.
During this period, CO2 warming was overtaken by an increase in human particulates and aerosol pollution. But, as pollution regulations and technology improved, sulphate aerosol concentrations decreased, human-C02’s warming effect re-emerged, and global warming continued apace. This “global dimming” effect does not negate the fact that the general trend is human-caused global warming.
In the natural cycle of 100,000 year long glacial periods and 10,000 year interglacial periods, we are and the very end of a 10,000 interglacial period. This is the peak where temperatures are at their peak in the natural cycles. At this peak, we are at something of a plateau. But, on this plateau, we are on a slow course to entering the next ice age. In fact, we were very gradually cooling over the length of the preindustrial Holocene at a slow pace of around a .5C reduction over 8000 years. While we should be on a cooling course, we are actually on a warming course. And, dramatically so. This should not be the case in the natural context, and is only explained by human activities.
“Leaving aside the descents into glaciation, which were much more gradual, the very sudden (geologically speaking) jumps up in temperature every ~100Kyrs actually represent a rate of change roughly ten times slower than the rate we are currently witnessing.”
Temperature and CO2 levels have varied widely throughout Earth’s cyclical patterns of 100,000-year-long ice-ages and 10,000 year-long inter-glacial warming periods. The Earth is currently peaking in an inter-glacial warming period, before it will, inevitably, enter the next 100,000-year ice age. It is natural to expect warming during this period.
The earth actually cooled between 1940 and 1975, contrary to human-caused global warming theory. Why would the earth cool during this period if anthropogenic global warming were occurring? 1940 to 1975 was a major period of unfettered industrial development.
How can we account for the warming of the Earth early in the century, from 1910 to 1940? At that time, the global emission of carbon dioxide from cars, trucks, and factories was relatively low–too low to account for the half-degree warming. Here also, natural factors in climate change, rather than human activities, must have been primarily responsible.
Some scientists note that global warming actually weakens the ability of the environment to absorb C02, thus making the planet even more susceptible to global warming. Given this “positive feedback loop”, it could be expected that natural global warming would lead to faster and faster rates of warming (acceleration). Therefore, it is not appropriate to credit all acceleration in warming to human-causes; this may be largely a natural phenomenon. And, the historical record does show sudden temperature spikes in history that would include a dramatic acceleration of warming due to natural causes.
Greenhouse gases are named as such because they have a “greenhouse effect” in the atmosphere, allowing sunlight to enter the earth’s atmosphere but trapping a percentage of the radiation that would otherwise be reflected back into space. The trapped radiation emits added heat into the Earth’s atmosphere with the result being “global warming”. The “greenhouse effect” is not disputed.
It is probable that the sun-earth interactions did lead to increased temperatures historically that caused melting of ice and other effects that caused increased CO2 emissions. BUT, these increased CO2 emissions then acted as “positive feedback loops” in increasing temperature. Nobody disputes that CO2 is a greenhouse gas that has a “greenhouse effect” on climate, so why would the fact that temperature lead CO2 in the historical record even matter? Is this supposed to indicate that CO2 is not a “greenhouse gas”? It certainly is, and is certainly acted as a “positive feedback” in the natural historical record.
Levels of greenhouse gases in the atmosphere have increased substantially through the industrial revolution. Sources cite that humans have contributed roughly 10 to 30 percent of the greenhouse gases that are currently in the atmosphere since large-scale industrialization began around 150 years ago. This substantial increase due to humans is certainly capable of producing the global warming effects we are seeing today. One of the reasons that the Earth’s atmosphere is so vulnerable to such a substantial increase in atmospheric greenhouse gases is that it is so thin.
While water is the most prominent greenhouse gas, it does not have a “forcing” effect on climate change.
The historical record shows that temperature changes have actually preceded C02 changes. This is demonstrated on the Vostok graph and shows that C02 changes could not actually be primary cause of global warming, or else they would have preceded temperature changes. This evidence would appear to indicate that global warming actually causes changes in C02 levels. Notable, in this fact, is that increases in CO2 levels cannot be wholly attributed to human-activities, as much if it is the side-effect of natural warming.
According to many sources, humans produce only single digit percentages of all the C02 that is released into the atmosphere every year. Volcanoes produce more than humans each year. This makes it impossible that humans are the main cause of global warming, even if we take greenhouse gases to be the main driver of global warming.
– Water vapor is the most potent greenhouse gas. It has had a major impact on global warming. And, as natural global warming occurs, and more ice melts, more water vapor enters the atmosphere, a “positive feedback loop” that adds to the natural acceleration of global warming.
“But sunspot-driven changes to the sun’s power are simply too small to account for the climatic changes observed in historical data from the 17th century to the present, research suggests. The difference in brightness between the high point of a sunspot cycle and its low point is less than 0.1 percent of the sun’s total output. “If you run that back in time to the 17th century using sunspot records, you’ll find that this amplitude variance is negligible for climate”‘…according to Solar astronomer Peter Foukal of Heliophysics, Inc.
and other researchers from the United States, Germany, and Switzerland found no net increase of solar brightness over the last thousand years. Solar cycles lead to a small increase of 0.07% in brightness over the last 30 years. This effect is far too small to contribute significantly to global warming.Foukal, Peter; et al. (2006-09-14). “Variations in solar luminosity and their effect on the Earth’s climate.”. Nature. Retrieved on 2007-04-16.A paper by Mike Lockwood and Claus Fröhlich found no relation between global warming and solar radiation since 1985, whether through variations in solar output or variations in cosmic rays. Henrik Svensmark and Eigil Friis-Christensen, the main proponents of cloud seeding by galactic cosmic rays, disputed the findings of Lockwood and Fröhlich.National Center for Atmospheric Research (2006-09-14).
Press release. Retrieved on 2007-07-13.
The argument here is that the sun has played the dominant role throughout history in determining the temperature of the earth.
Some graphical analyses of sun variations and global temperatures reveal a very tight relationship through history. This graphical correlation is really the main argument here. The question is, does the sun’s relationship to temperature correlate more strongly than the relationship of greenhouse gases and global temperature? This side of the argument makes the point that it does.
This is a major demonstration of the inter-planetary effect that the sun is having on climates. The problem of global warming is not reserved solely to the Earth at this time. In fact, the trends on Mars match closely what is occurring on Earth. The only common factor between Mars and the Earth is the Sun. This seems to demonstrate the the sun is a central force driving Earth’s climate change.
“The spatial pattern of where this warming is occurring around the globe indicates human-induced causes.”
Satellite temperature measurements show that tropospheric temperatures are increasing with “rates similar to those of the surface temperature,” leading the IPCC to conclude that this discrepancy is reconciled. (see argument page for more)
Global warming is occuring and this is indeed resulting in the melting of ice-bergs and so-forth. Yet, this does not necessarily demonstrate human causes. Natural warming in Earth’s history has resulted in such melting and on-the-ground climate changes.
Global warming produces many on-the-ground effects that add, in turn, to additional global warming. These are known as “positive feedback loops” and include such things as the depleted ability of forests to act as carbon-sinks as well as the added heat absorption of the oceans due to the melting of ice (more dark, non-reflective surface area). These effects can accelerate global warming and thus accelerate the effects of global warming on the ground. This makes it difficult to assume that accelerating on-the-ground effects from global warming demonstrate human-causes; they could be part of natural causes.
Images are often presented that attempt to show the recession of both, and are held up as demonstrations of human-caused global warming. But, what is essential is that these images are taken in the appropriate context. If an image from the past from the middle of the winter is compared with a present image taken during summer months, than this is a faulty comparison; the comparison needs to be made in the same months of the year between different years.
If greenhouse gases were causing the climate warming then scientists would expect the troposphere to be warming faster than the surface, but observations do not bear this out
A very extensive outline of the “scientific consensus” that it is very likely that most of global warming can be attributed to human activities.
“The detailed causes of the recent warming remain an active field of research, but the scientific consensus identifies elevated levels of greenhouse gases due to human activity as the main influence.”
“There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.” 
– “How strong is the scientific consensus? Back in 2001, President George W. Bush asked the National Academy of Sciences for a report on climate change and on the conclusions of the IPCC assessments on climate change. The eleven member blue-ribbon panel, which included experts previously skeptical about global warming, concluded: Temperatures are rising because of human activities; the scientific community agrees that most of the rise in the last half-century is likely due to increased greenhouse gas concentrations in the atmosphere; and ‘the stated degree of confidence in the IPCC assessment is higher today than it was 10, or even 5 years ago.'”
“Earth is currently experiencing rapid warming, which the vast majority of climate scientists says is due to humans pumping huge amounts of greenhouse gases into the atmosphere.”
“The world’s leading climate scientists said global warming has begun, is very likely caused by man, and will be unstoppable for centuries, … . The phrase very likely translates to a more than 90 percent certainty that global warming is caused by man’s burning of fossil fuels. That was the strongest conclusion to date, making it nearly impossible to say natural forces are to blame.”
New Scientist notes that in surveys a much larger fraction of U.S. scientists consistently state that they are pressured by their employers or by U.S. government bodies to deny that global warming results from human activities or risk losing funding.
Al Gore’s “An inconvenient truth” – Out of 928 peer-reviewed articles, all of them concluded that humans are the cause of global warming.
Many members of the scientific community, and climatology branch of the scientific community, are skeptical that humans are the chief cause of global warming or deny this notion all together.
“Since I obtained my doctorate in climatology from the University of London, Queen Mary College, England my career has spanned two climate cycles. Temperatures declined from 1940 to 1980 and in the early 1970’s global cooling became the consensus. This proves that consensus is not a scientific fact.”
The IPCC report should not be trusted.
The conclusions are politically motivated.
Fredrick Sites, former president of the National Academy of Sciences.
“I have never witnessed a more disturbing corruption of the peer review process than the events that led to this IPCC report.”
“this report is not what it appears to be – it is not the version that was approved by the contributing scientists listed on the title page.”
“None of the studies cited has shown clear evidence that we can attribute the observed [climate] changes to the specific cause of increases in the greenhouse gases.”
Money is often directed toward studies that could be considered interesting or dramatic. This creates a financial incentive for scientists to “find” dramatic global warming effects. Because the prevailing opinion is that global warming is human-caused, there is an interest in seeing articles published that support this view. Some even suggest that scientists are tweaking their computer models so that the results show a more dramatic relationship between human activities and temperature changes than actually exists.
Many businesses are benefiting from the global warming crisis. Solar energy, for example, has a direct interest in seeing the propagation of the notion that global warming is human caused.
The media is representing the scientific consensus that humans are the primary cause of global warming in the modern era. This consensus should be relied-upon by journalists; what basis do they have to doubt it?
There are no legitimate arguments against the resolution that climate change is chiefly human-caused. To admit that these arguments have any validity whatsoever shows bias in the media.
A new generation of environmental journalists has emerged whose jobs are dependent on the existence of the Global Warming crisis.