Is the world’s climate changing and is it our fault?

Let’s check the science: Is it true that human activity is driving serious global climate change?

I’ve been aware of the potential dangers of global warming since the late 1970′s. Since that time, I’ve seen the scientific evidence for the consequences of burning fossil fuels accumulate and I’ve become increasingly concerned. But in the media, I encounter people (admittedly none of them with any expertise in the field), who vehemently deny that the situation exists. They do not convince me, but they make me wonder how anyone can hold such positions in the face of overwhelming evidence. In an attempt to appreciate the magnitude of their foolishness, I think it’s time to remind myself how convincing the evidence for human-induced climate change is.

The promoters’ arguments – science or red flags?

Basically, the scientific argument is this: greenhouse gases, released primarily by human activities, are causing the earth to accumulate heat energy; this, among other consequences, will result in drastic changes in global climate. In technical terms, it’s known as anthropogenic climate change.

There’s a long history to this argument. It starts in 1896 with the Swedish scientist Arrhenius, who worked out that adding carbon dioxide to the atmosphere would result in global warming. About the middle of the 20th century, scientists started getting concerned about the possible dangers this posed and the number of scientific studies on the topic started to build up. At that early stage, there was no consensus though, because some scientists thought that the earth could be heading into a cooling phase. By the 1970′s, it was becoming obvious that the earth was indeed on a warming trend. Scientists started to look for evidence to show what was causing the warming and began making projections about the consequences. There are now thousands of scientific papers examining the phenomenon. (For more detail, see the excellent histories by John Mason at Skeptical Science or Spencer Weart, here.)

As long as you stick to the peer-reviewed scientific literature, red flags are few and far between on this topic. On the contrary, all the hallmarks of science are there: there is a variety of models; they are tested in the real world; there is a coherent body of knowledge that is supported by peer review; but it is acknowledged that there gaps in our knowledge.

Unfortunately, outside the scientific literature, many red flags appear.

The doubter’s arguments – science or red flags?

Those who doubt the scientific argument do so on three main grounds; that the earth is not accumulating heat energy at all (see here); or, that the warming and climate change are caused not by humans, but by natural cycles (see here and here); or, that any change caused by human activities will be minor (see here). None of these positions is supported by the science. Recently, the science writer James Lawrence Powell surveyed the peer-reviewed scientific literature from the last 21 years. He found that there had been 13,950 papers on global warming or climate change published in that period. Only 24 of those papers (that’s 0.17 per cent) attempted to reject the model of human-caused global warming. The details of Powell’s study are here.

Doubters of the scientific position are prolific producers of red flags. The main ones used are cherry picking (see here), conspiracy theories (see here), the Galileo gambit (see here), appeals to authority (see here) and single-study syndrome (see here). Skeptical Science deals with the whole gamut of the doubters’ PRATT list (here).

Being skeptical

On the basis of red flags, I’m extremely skeptical about the doubters’ claims. This doesn’t excuse climate scientists from supplying supporting evidence though – that would be switching the burden of proof. So I need to look for trustworthy sources of evidence supporting the anthropogenic climate change model. At the same time, I should examine any evidence the doubters present to support any scientific models they propose.

There is also plenty evidence that most doubters are operating from ideological bias or financial interests.  Naomi Oreskes and Erik M. Conway give lots of detail in their 2010 book Merchants of Doubt, and there have been many other studies demonstrating the links – see here, here, here and here. A good summary of the tactics used can be found at DeSmogBlog.

The scientific evidence

Until the 1970′s, the evidence for human-induced climate change was not conclusive. Since then, evidence in support of the model has continued to accumulate. It would be impossible for me to look at all of the peer-reviewed papers on this issue, but fortunately I don’t need to.

The most reliable snapshots of the current state of scientific knowledge on any topic are provided by systematic reviews. In the case of climate change, the Intergovernmental Panel on Climate Change (IPCC) conducts massive systematic reviews about every five or six years. Here’s how the IPCC’s own website describes its role:

The Intergovernmental Panel on Climate Change (IPCC) is the leading international body for the assessment of climate change. It was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to provide the world with a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts. In the same year, the UN General Assembly endorsed the action by WMO and UNEP in jointly establishing the IPCC.

The IPCC is a scientific body. It reviews and assesses the most recent scientific, technical and socio-economic information produced worldwide relevant to the understanding of climate change. It does not conduct any research nor does it monitor climate related data or parameters.

Thousands of scientists from all over the world contribute to the work of the IPCC on a voluntary basis. Review is an essential part of the IPCC process, to ensure an objective and complete assessment of current information. IPCC aims to reflect a range of views and expertise.

I’ve bolded one paragraph in the above quote because the role of the IPCC is frequently misrepresented by doubters. It’s important to realise that the IPCC reviews the work of scientists worldwide – it does no research of its own.

The IPCC is not perfect, but it is by far the most trustworthy body to consult for reliable information about climate change. Its most recent reports were published in 2007, and the evaluation of the scientific evidence can be found in the report titled “The Physical Science Basis“. From that report, here are the “robust findings” that are most relevant to the question we are checking on here:

• Current atmospheric concentrations of CO₂ and CH₄, and their associated positive radiative forcing, far exceed those determined from ice core measurements spanning the last 650,000 years.

• Fossil fuel use, agriculture and land use have been the dominant cause of increases in greenhouse gases over the last 250 years.

• The sustained rate of increase in radiative forcing from CO₂, CH₄ and N₂O over the past 40 years is larger than at any time during at least the past 2000 years.

• From new estimates of the combined anthropogenic forcing due to greenhouse gases, aerosols and land surface changes, it is extremely likely that human activities have exerted a substantial net warming influence on climate since 1750.

• Solar irradiance contributions to global average radiative forcing are considerably smaller than the contribution of increases in greenhouse gases over the industrial period.

There has been much more evidence since 2007, and it shows overwhelmingly that anthropogenic climate change is real. It is now quite obvious that the IPCC has been very conservative in its findings. The next IPCC reports, to be published in 2013, will undoubtedly display even greater conviction that human-induced climate change is happening and that it’s serious.

The small number of scientific papers that doubt human-induced climate change is taken into account by the IPCC reviewing process. As we can see from the IPCC findings, none of these papers has presented evidence that is compelling enough to overturn, or even significantly effect, the accepted model. One of the most popular of the doubters’ claims, that variations in solar radiation are important, is addressed and discounted by the last of the points above.

(Update 2013/05/16: For those who are reluctant to accept the IPCC interpretation, here are some independent reviews:

 The scientific consensus on climate change
(Naomi Oreskes, 2004)

The scientific consensus on climate change: how do we know we’re not wrong?
(Naomi Oreskes, 2007)

Examining the scientific consensus on climate change
(Peter Doran & Maggie Zimmerman, 2009)

Expert credibility in climate change
(William Anderegg, James Prall, Jacob Harold & Stephen Schneider, 2010)

Quantifying the consensus on anthropogenic global warming in the scientific literature
(Cook et al, 2013))

DIY evidence

It’s tempting to make your own judgement about climate change from your own experience. To many of us, it seems that there have been obvious shifts in local climate since our younger days. But it’s dangerous to draw conclusions from our own limited knowledge. Humans are notoriously bad at making correct statistical judgments from personal experiences. Only long-term observations from all over the globe can give valid data about climate change.

Conclusion

It’s clear to me that the scientific evidence leaves no room to doubt. The anthropogenic climate change model is robust. This does not mean that the model is perfect nor that there is nothing more to be discovered. There are uncertainties, and the IPCC reports go to great lengths to describe what those uncertainties are. Doubters like to exploit the uncertainties in attempts to make the findings appear shaky, but this tactic has no traction within the scientific community. Never has a branch of science been scrutinised as closely as climate science, yet its conclusions remain solid. The science is clear: multiple independent lines of evidence show that we are causing climate change – and it’s serious!

Update 2013/01/04: Climate scientist Katharine Hayhoe has an article on this very topic here. It’s very clear and easy to follow.

Update 2013/05/13: Here’s Peter Hadfield’s excellent video The evidence for climate change WITHOUT computer models or the IPCC. It’s an easy-to-follow summary of the long-standing evidence which shows that atmospheric carbon dioxide has always influenced global temperature.

Tropical Cyclone Inigo approaching northwest Australia photo by Jeff Schmaltz, MODIS Rapid Response Team, NASA/GSFC (http://visibleearth.nasa.gov/view_rec.php?id=5161) [Public domain], via Wikimedia Commons

This is one of ScienceOrNot’s Let’s check the science series.