Louis Hissink has recently (18/8) tried to portray the finding that carbon  dioxide levels are rising more quickly than expected as irrelevant, and cast  doubts on the whole theory of human induced global warming.

For those who have followed the debate Hissink's style of argument was  familiar. Lots of snide comments, references to "junk-science" and plenty of  implication that belief in anthropogenic global warming is restricted to  hard-line environmentalists and a minority of scientists. Crucially, it  takes a single piece of evidence in regard to global warming and implies  that it stands on its own and therefore means nothing.

Nothing could be further from the truth. The belief that the release of  gasses into the atmosphere through human activity is warming the planet -  commonly, and not entirely correctly, known as the Greenhouse Effect - is  one of the most widely researched and supported theories in modern science.  It depends on research in areas including meteorology, oceanography,  geology, palaeontology, astronomy and biology. Outside geology it is hard to  find a credible scientist in any of these areas who does not believe it. The  most respected scientists from other fields (measured for example by Noble  Prizes) are also overwhelmingly in agreement on both the existence, and  seriousness, of the problem.

The Anthropogenic Global Warming Hypothesis (AGWH) is like a jigsaw. There  are literally tens of thousands of pieces of research - all pieces of the  puzzle slowly being fitted together. The report on the surprisingly rapid  growth in CO2 levels over the last two years is one piece, and not the  largest. On it's own it means little, but in combination with the rest it  points to an increasingly clear and frightening picture. To take it out of  context of this other research, and indeed suggest the other research does  not exist is misleading, if not outright dishonest.

It's true that now and then some research appears to contradict the AGWH.  Sometimes the work turns out be deeply flawed for one reason or another -  often such research is funded by coal or petroleum industries. On other  occasions the results remain a puzzle. However a few dozen counter  indications don't mean a whole lot, when set against the vast and growing  volume of peer reviewed research supporting AGWH.

To take the specifics of Hissink's case. He starts off with a lot of blather  about how people can be scared by figures of 400ppm CO2 in the atmosphere, when this is currently 378 ppm, and that this can be written as 0.000378 or  rounded off inappropriately. All true (other than the point where he says it  will take us 22 years to hit 400 ppm - the true figure, based on an increase  of 2ppm per year, is 11 years) but not very important. Even one part per  million of a particularly toxic gas can be fatal. The important thing is the  potency of the substance in question.

However, the real flaw in Hissink's piece is where he suggests that CO2 does  not cause warming because of "when CO2 goes down in concentration, the  temperature goes up!". Various theories and questions are proposed,  including the classic "This suggests that CO2 is much like a migratory bird,  moving around the planet to colder areas, and I suppose some po-faced  scientist will, in all seriousness, confirm this to be fact".

There is actually not mystery. The answer is widely available on the web,  and taught in undergraduate meteorology degrees. Trees grow by absorbing  carbon dioxide from the atmosphere. To do this they need sunlight. In  temperate regions they restrict their growing to months with more sunlight.  The effects are called leaves, flowers and new branches. All of these are  made to a substantial extent of carbon previously circulating in the  atmosphere.

Most of the southern hemisphere temperate zone is ocean, while much of the  northern belt is land. Consequently there is far more annual growth during  the northern summer, and at this time CO2 levels in the atmosphere drop.  Without human contribution they would go back up to around the original  point in winter as leaves drop and rot. Human emissions however are meaning  that year on year the levels have been rising, and the recent research  suggests that this rise is accelerating.

Hissink suggests that the fact that CO2 levels at Hawaii are lower when the  temperature is higher conflicts with the theory CO2 raises the temperature.  In fact both are caused by increased sunlight in the northern hemisphere.

The discovery that certain gasses, particularly carbon dioxide, trap heat  close to the Earth rather than letting it escape to space dates to the  nineteenth century - doubting it puts you in the same league as the  flat-earthers. The June-August fall in CO2 levels does make the planet  slightly cooler than it would be otherwise, but the fall is so small (three  percent at most) that it is totally overwhelmed by other factors, such as  the way land masses warm up more quickly than oceans.

Given that the physics of how carbon dioxide traps heat was solved over a  hundred years ago, the crucial question in studies of the AGWH is how much  will raising CO2 levels in the atmosphere warm the planet. Estimates  published in the 1970s ranged from trivial fractions of a degree to double  figures for a doubling of CO2 levels. Time and greater research have  narrowed this range, so there is now increasing consensus that, unless  significant action is taken, we are facing warming sufficient to make this  issue one of the most important facing humanity.

Note: I am not an expert in many (arguably any) of the areas contributing to  AGWH. One of the reasons why attacks such as Hissink's often go unchallenged  is that most scientists working on AGWH lack confidence, lest they be  challenged on an aspect of the theory they are personally not very familiar  with. I believe this reticence needs to be broken, so I'm replying although  I can't speak with confidence on all areas.