Wednesday, July 25, 2012

Droughts and flooding rain

A couple of years ago, I used to notice - amongst the usual flotsam and jetsam of half-baked semi-truths, muddled confusion, conspiracy theories, ideological axes, pay-per-comment outright deception and opportunistic spin that passes for much of online climate science dissent - some commenters mocking the idea that a warming world might bring both more droughts and more floods. Now some managed to get past the initial intelligence test by realising that one location might get wetter while another becomes drier, but the second hurdle was realising that the mainstream prediction is (and has been for some time) that in some instances, increased droughts and increased flooding might be likely to occur in the same location.

But today - after the severe Australian drought of the naughties being followed by the wettest 24 months on record, a rare hosepipe ban and widespread drought in England followed by the wettest April and June on record and last year's record Mississippi floods prior to recent reports of grounded barges from river levels 15m lower than a year ago - I don't seem to hear that comment much anymore.

A warming world doesn't just mean a hotter world, but one capable of all kinds of greater extremes.
Image by JKS.


Anonymous said...

James Hansen explained one powerful factor and that is every degree warmer, the atmosphere can carry 5% more moisture. That enables 5% more drying in one place and dumping in the next. When you consider that while the global averages are for 2 degrees of warming but this warming will be far more concentrated on the Northern Hemisphere (because of where the continents are?), then the LOCAL temperatures will be much higher.

David Coleman said...

Yes, paradoxically another effect of climate change which is difficult to comprehend at first is that some parts of the world may actually get much colder. As an example, the melting of the polar ice caps could lead to the diversion of the Gulf Stream southward, robing northern europe of its warming ocean currents during that time of the year and actually leaving the the British, French and the Germans out in the cold rather than warming them up.

byron smith said...

Dave - Yes, 2ºC global rise equates to something like 6ºC or more in the Arctic (and less than 1ºC over much of the oceans). And remember that on our current trajectory, we're heading for far, far more than 2ºC in the absence of very, very aggressive mitigation efforts in the very near future.

David - That particular mechanism has been theorised for some time, but the reality is likely nothing nearly as dramatic as The Day After Tomorrow, which is one of those "friends" that you wish would just go away for all the extra confusion they spread. Parts of Europe may warm at a somewhat slower pace than other land areas, but very few researchers think we're going to see a sudden ice age descend on Europe. Remember, shifting ocean currents don't affect the global heat budget, just its distribution, so if somewhere is warming at a slower pace than average, that means other places are warming above the average.

byron smith said...

The Conversation: A land of more extreme droughts and flooding rains. First in a series on climate and water in Australia. Excellent.

byron smith said...

Preserving a comment I just wrote on FB answering a question about ENSO:


The ENSO cycle is a short-term (3-7 year) shifting of the planet's heat around from one place to another via ocean currents. Anthropogenic warming is a long term increase in the total heat content of the planet. So in a warming world, both El Niño and La Niña get warmer, even though La Niña dominated years are likely to be, on average, cooler than El Niño years. To illustrate, notice that 2011 was dominated by a La Niña phase of the cycle, and so was cooler than 2010, (which was dominated by a mild to moderate La Niña). But 2011 was warmer *than every other La Niña on record*. Another illustration: 1998 was a record-breaking hot year, statistically tied in most data sets with 2005 and/or 2010 (the three were all very close to each other in all data sets). But 1998 was dominated by a super El Niño, one of the largest seen in a long time, while 2005 and 2010 were only mild to moderate El Niño years.

By the way, when I speak about warmer and cooler, I'm talking about global surface temperatures, which is not at all the same thing as the global heat budget (total amount of heat energy in the planet's system). The latter includes heat energy in the soil and, crucially, oceans (as well as the energy required for phase shifts, like melting ice). See this useful infographic.

So, at the risk of oversimplifying a very complex process, the extra heat being trapped in the planetary system (added to the system) increases with only relatively minor variations, year on year. All the time, the vast majority of this energy is going into the oceans. In fact, the radiative forcing from human emissions is the equivalent of adding the energy of more than ten Hiroshima bombs every second to the planet, and more than nine of these go into the oceans. During La Niña conditions, slightly more of this incoming energy ends up being stored in the oceans and during El Niño conditions, slightly more is shared with the atmosphere. So if we're only looking at atmospheric temperatures, we're really only seeing part of the picture.

byron smith said...

Tamino illustrates the increased likelihood of extreme events with some fairly straightforward statistics and a dice analogy.

Simon said...

What gets me is all the records that have been broken and we are still just coming out of a solar minimum. Now thats scary.

byron smith said...

Simon - Indeed, and we're had more aerosol negative forcing than at any time since the 50s and 60s due to the explosion of Chinese coal plants.

Simon said...

Byron if there is a silver lining it is that for many people their views on climate change hinge on current weather patterns; so when we come out of the cooling and they start to get a taste of real heat we will start to see some momentum for change.

Secondly I imagine that when they have to face this people's natural tendency to scapegoat and blame others, we will see them turn on climate deniers and corporate funders.

byron smith said...

Pennsylvania report: When it rains, it pours. Extreme precipitation events on the rise.

byron smith said...

Planet 3.0: Some recent journal papers on extreme weather.

byron smith said...

Conversation: Observations show rising global precipitation. The authors include some important caveats against overly simplistic readings of their data:

"Nevertheless our analysis should not be interpreted as suggesting that the rapid increase in flood damage which has occurred over the past few decades is entirely attributable to climate change.

"In fact, other changes such as deforestation, rapid urbanisation and an increase in the number of people living in flood plains are likely to account for the bulk of these changes. Furthermore, not all floods are caused by extreme rainfall events. Snow melt and storm surge also contribute to overall flood risk. Antecedent moisture – the wetness of the catchment prior to the flood-producing rainfall event – can also have a substantial influence on flood risk. In some parts of Australia this might even cause flood risk to decrease because of an expected increase in the number or severity of future droughts.

"Despite all these caveats, our recent study contributes to the debate on how climate change will affect flood risk, by showing that the intensification of rainfall extremes is not just a projection made by climate models. Rather, it can already can be detected in our observational record."