Monday 21 May 2012

What is a change in extreme weather?

What is a change in extreme weather?

The reason for changes in extremes can be divided up into two categories: changes in the mean (see panel a of the figure below) and other changes in the distribution (simplified as a change in the variance in panel b). Mixtures are of course also possible (panel c).

If you are interested in the impacts of climate change, you do not care why the the extremes are changing. If the dikes need to be made stronger or the sewage system needs larger sewers and larger reservoirs, all you need to know is how likely it is that a certain threshold is reached. Much research into changes in extreme weather is climate change impact research and thus does not care much about this distinction.

If you are interested in understanding the climate system, it does matter why the extremes are changing. Changes in the mean state of the climate are relatively well studied. Interesting questions are, for instance, whether a change in the mean changes the distribution via feedback processes or whether the reduced temperature contrasts between the poles and the equator or between day and night cause changes in the distribution.

If you are interested in understanding the climate system also the spatial and temporal averaging scales matter. If rain fronts move slower, they may locally produce more extreme daily precipitation sums, while on a global scale or instantaneously there is no change in the distribution of precipitation.

I hope scientists will distinguish between these two different ways in which extremes may change in future publications and, for example, not only compute the increase in the number of tropical days, but also how many of these days are due to the change in the mean and how many are due to changes in the distribution. I think this would contribute to a better understanding of the climate system.

Figure is taken from Real Climate, which took it from IPCC (2001).

Saturday 19 May 2012

Paleo and fruitarian lifestyles have a lot in common

My new fitness trainer eats a lot of fruit. And she looks darn healthy. Now I know, you should not take weight-training advice from a professional body builder or risk serious overtraining, but still I was intrigued and did some research. The vegan and paleo communities are often not on friendly terms. Thus what struck me most researching fruitarian blogs, was how similar many of the ideas were.

A very strict fruitarian only eats fruits in the common meaning, sweet and juicy fruits from trees or bushes. Others also include vegetable fruits such as avocados, tomatoes and cucumbers, still others also include nuts, many regularly eat salad. To get sufficient calories from fruits, a fruitarian has to eat several kilograms of fruit. Some people calling themselves fruitarians actually get most calories from nuts and avocados. In this post fruitarians are people getting most calories from simple carbohydrates, that is from sweet fruits.

The paleolithic lifestyle is inspired by the way people lived before agriculture. As the information from the Paleolithic Age is scarce, in praxis this often means, that existing hunter gatherers and their diets and lifestyles are studied. Such bands often trade with nearby agriculturalists and thus no longer live a true stone-age life. Still as long as they are free from the deceases of civilisation, they provide good role models in my view. Similarly, many paleos also look at other existing cultures that are in good health. In this respect the paleo community is close to the Weston A Price Foundation, who seek guidance with how people lived a few generations ago. The paleo diet is best defined by what it not eaten: processed foods, grains, sugar and refined seed oils.