One of the most important concepts to understand when trying to grasp how the Earth's climate works, is that every climate change must have a physical cause. This principle was the basis of our new paper, Nuccitelli et al. (2013). Over the past century, climate scientists have developed a solid understanding about how the climate works and the physical mechanisms that cause it to change. By building that knowledge into complex climate models, scientists have been able to accurately reproduce past observed global surface temperature changes.

Global mean near-surface temperatures from observations (black) and as obtained from 58 simulations produced by 14 different climate models driven by both natural and human-caused factors that influence climate in the 2007 IPCC report (yellow). The mean of all these runs is also shown (thick red line). Vertical grey lines indicate the timing of major volcanic eruptions.

It's not sufficient to say global warming is the result of "a natural cycle" – which cycle is causing the change? For example, is it due to the Earth's orbital cycles around the Sun, which operate very slowly over periods of thousands of years? Is it changes in solar activity, which has on average remained flat and even declined slightly over the past 60 years? Is it ocean cycles, which shift heat between the oceans and air, and don't cause the Earth to accumulate more heat?

Recently, a brand new scientific journal called Climate published a paper by Syun-Ichi Akasofu, a retired geophysicist and former director of the International Arctic Research Center at the University of Alaska-Fairbanks. Despite having a background in physical sciences, Akasofu made a very unphysical argument in that paper. He claimed that the current global warming is merely a result of the planet "recovering" from the Little Ice Age – a cool period (the cooling mostly isolated in Europe) that lasted between the years of about 1550 and 1850.

Problem – Akasofu didn't identify any physical cause for this supposed 'recovery.' Instead he engaged in what's known as "curve fitting," in which you take data that is correlated to your desired graph and scale it to match, then argue you've proven that your data is the cause of the changes shown in that graph. In other words, it confuses correlation with causation. If I can take data regarding the number of pirates in the Caribbean and consumption of spaghetti in Ireland and make it fit the global temperature data, that doesn't mean that pirates and Irish spaghetti are causing global warming. A physical cause must be identified.

Akasofu didn't do that. He just roughly fit some ocean cycle data to the global surface temperature measurements and decided that a linear warming trend was left over. He then declared that linear trend was the "recovery" from the Little Ice Age, and that it would continue indefinitely into the future, despite not knowing its cause.

Unfortunately the peer-review process isn't perfect. It's necessary but insufficient in separating the good from the flawed research. Sometimes a bad paper will slip through the cracks, whether due to a poor choice of reviewers, or the judgment of the journal editor. Akasofu's paper was published in the very first edition of Climate, which caused great concern amongst its editorial staff (many of whom recognized the poor quality of the paper), and even caused one editor to resign from the journal.

In fact, Akasofu had published a very similar paper in another journal in 2009, which I had debunked at the climate science website SkepticalScience.com. John Abraham suggested that we should submit a comment to the journal based on the same points I had made in that post, and so we did, with input from our co-authors Rasmus Benestad and Scott Mandia.

The main point we made in our recently published paper was that Akasofu merely engaged in a curve-fitting exercise and failed to account for any of the known physical causes of the global energy imbalance, such as the increased greenhouse effect. Instead, Akasofu's argument was essentially based on magical thinking – claiming that the Earth's climate is just "recovering" on its own from the Little Ice Age, and assuming that this "recovery" will continue indefinitely.

Akasofu's paper was also based on the false premise that global warming has "halted." In reality, just the warming of surface temperatures (which only represent about 2 percent of overall global warming) has slowed over the past 10–15 years. Akasofu failed to reference the many studies that have accounted for the warming of the entire climate (oceans, air, ice, and land) and have shown that if anything, global warming is accelerating. Many of these papers have also shown that the slowed warming of surface temperatures is consistent with the accelerated warming of the oceans we've seen over the past 15 years.

Global heat accumulation data (ocean heating in blue; land, atmosphere, and ice heating in red) from Nuccitelli et al. (2012)

The problem with many anything but carbon (ABC) climate contrarian hypotheses like Akasofu's is that they throw out what we know about how the Earth's climate works. It's fine to try and account the influences of ocean cycles – that's what mainstream climate scientists are doing – but we've known how the Earth warms in response to the increased greenhouse effect for over a century. We also know that any long-term global warming must be caused by a global energy imbalance.

Any valid climate research has to work within that known framework. When you throw out everything we know about the Earth's climate, you're stuck making unphysical arguments based on nothing more than correlations and curve fitting, as Akasofu did. The problem for climate contrarians is that our existing climate framework is very solid. We understand the fundamentals about how the climate operates well enough to accurately reproduce the observed changes, based on solid, well-understood physical mechanisms like the increased greenhouse effect. That's not about to get overturned by magical thinking.