Posts Tagged ‘James Hansen’

I told you so

October 20, 2012
In 1981 Hansen et al made predictions for the change in global mean temperature expected over the course of the coming century. The figure shows their predictions along side 4 independent estimates of what has actually happened.

In 1981 Hansen et al made predictions for the change in global mean temperature expected over the course of the coming century. The figure shows their predictions along side four independent estimates of what has actually happened.

According to Gore Vidal, the four most beautiful words in the English language are “I told you so”. My hero James Hansen can justifiably speak those words, but I am sure they don’t feel beautiful to him.

In 1981, together with six NASA colleagues, he published a paper in Science magazine entitled ‘Climatic Impact of Increasing Atmospheric Carbon dioxide‘. Science magazine won’t let you read it but it is available online here. The paper is not that difficult to understand and if you are curious about these things, it’s a good read. I particularly liked the inclusion of a simple analogy:

“The surface temperature resulting from the greenhouse effect is analogous to the depth of water in a leaky bucket with constant inflow rate. If the holes in the bucket are reduced slightly in size the water depth and water pressure will increase until the flow rate out of the holes once again equals the inflow rate. Analogously, if the atmospheric infrared opacity  increases, the temperature of the surface and the atmosphere will increase until the emission of radiation from the planet again equals the absorbed solar energy.”

The figure at the top of the page shows Figure 6 from their paper on which I have overlaid four independent estimates of what has actually happened since then. At the time the paper was published,  global mean temperature was declining and the predictions were thus extremely bold. However, looking back the authors predictions now seem conservative. And indeed the authors were careful and conservative, though clear about specific predictions.

In the summary they state

“Potential effects on the climate in the 21st Century include the creation of drought-prone regions in North America and central Asia … erosion of the West Antarctic Ice Sheet … and an opening of the fabled NorthWest passage”

Well, North America has been prone to drought, and the North West passage now regularly opens in summer. Thankfully the West Antarctic Ice Sheet seems relatively stable.

All through the paper the authors consider the uncertainties arising from the simplicity of their model and the many poorly-understood effects – such as cloud cover and solar variability – which affect climate. However, they test their predictions against plausible variations in these factors and find that the predictions of warming are robust against a wide range of plausible feedback effects. They conclude with a wider non-scientific perspective

Political and economic forces affecting energy use and fuel choice make it unlikely that the CO2 issue will have a major impact on energy policies until convincing observations of global warming at in hand. In light of historical evidence that it takes several decades to complete a major change in fuel use this makes large climate change almost inevitable.

However the degree of warming will depend strongly on the energy growth rate and the choice of fuels for the next century. Thus CO2 effects on climate may make full exploitation of coal resources undesirable. An appropriate strategy may be to encourage energy conservation and develop alternative energy sources while using fossil fuels as necessary during the next few decades.

The Climate change induced by anthropogenic release of CO2 is likely to be the most fascinating global geophysical experiment that man will ever conduct. The scientific task is to help determine the nature of future climatic effects as early as possible. The required efforts in global observations and climate analyses are challenging, but the benefits from improved understanding of climate will surely warrant the work involved.

To me these views seem modest, realistic and optimistic. But I bet that although James Hansen and his colleagues predicted the climate 30 years ahead, they never guessed that in the 21st Century the US would have senators such as Paul Brown.

To understand such ignorance we have to turn again to Gore Vidal:

The United States was founded by the brightest people in the country – and we haven’t seen them since.

Acknowledgement: This article is based on a blog story at Real Climate:

If Global Warming is happening, when will I be able to notice?

August 27, 2012
Probability of June, July and August average temperature anomalies in Moscow, Russia since 1950. This image shows that the average temperature in Moscow for summer 2010 was significantly hotter than in any year since 1950. Credit: Claudia Tebaldi and Remik Ziemlinksi.

Probability of June, July and August average temperature anomalies in Moscow, Russia since 1950. This image shows that the average temperature in Moscow for summer 2010 was significantly hotter than in any year since 1950. Credit: Claudia Tebaldi and Remik Ziemlinksi. From Climate Central

What Is The Climate? A Science Song by Tom Glazer

Climate Change is slow on the scale of a human lifetime, and small in comparison with day-to-day and season-to-season variability. A change of average summer temperatures by 1 °C over 10 years is small compared to a day-to-day variability of typically ±5 °C in the course of a typical summer.

So we rely on meteorologist, and climatologists and statisticians to tell us when ‘something is happening’. However many people are understandably sceptical of the opinion of ‘experts’. In many areas – for example in the field of human nutrition – expert opinion is fickle and changeable. So at what point can we expect to be able to make up our own minds using our own senses?

That is the question addressed by James Hansen in a paper (Perception of climate change: pdf: open access) published by the National Academy of Science (of the United States of America).The paper considers extremes of weather and in particular, hot summer events in the Northern Hemisphere. I am not sure that the paper completely answers the question it sets out to answer, but nonetheless is it is very readable.

The conclusion of the paper is shocking. Compared with a reference period from 1950 to 1980, extremely hot summers in the Northern Hemisphere land area are now more than ten times as common. In a typical recent summer, these anomalous conditions now exist over 10% of the Northern Hemisphere land area, compared with a few tenths of a percent in the reference period.

Hansen concludes that these events (e.g. the current US drought , the Russian heatwave in 2010) are now so commonplace that they can they can definitely be said to be due to a changed climate. The extreme summer events arise not just from the warming trend, but also an increase in climate variability – essential extreme weather – compared to the locally-expected average weather. NASA have prepared a nice animation here.

Hansen is clearly convinced, and he convinces me. But other aspects of the changed climate conspire against the perception of change. For example if cold dry winters are replaced by not-so-cold but snowy winters, then people perceive those as being ‘worse’, even if the actual temperatures are higher.

Hansen is addressing this issue for a reason. It is not until the majority of people in a democracy become personally convinced that the Climate really is changing, that it will become inevitable that politicians will do something. Reducing greenhouse emissions – mainly carbon dioxide – is not fun for anyone. But if the US loses a significant fraction of its corn crop for more than a year or two in a row, then even the denialists and contrarians may think again.


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