Chris Vernon

It’s been a while since I last posted an interesting chart. Here’s another one. I first came across it in a lecture I attended titled “Ocean Circulation and Climate” given by Helen Johnson last year. The chart was produced by Stefan Rahmstorf, a version is included in the following paper, available on his website:

Rahmstorf, S. and A. Ganopolski, 1999: Long-term global warming scenarios computed with an efficient coupled climate model. Climatic Change, 43, 353-367.

Deviation of the annual mean surface air temperature from its zonal average - Rahmstorf (1999)

The provided caption reads:

Deviation of the annual-mean surface air temperature from its zonal average, computed from the NCAR air temperature climatology. Anomalously cold areas are found over some continental regions, anomalously warm areas over ocean deep water formation regions.

The term “zonal average” means the average along a line of latitude. Meridional refers to longitude (think Greenwich Meridian). The chart shows that the average air temperature off Scandinavia is some 10 °C warmer than the average temperature at the latitude (60 to 70 degrees North). NCAR refers to The National Center for Atmospheric Research.

Rahmstorf explains in his paper how this temperature deviation is the result of heat being transported by ocean currents, currents that do vary over time and could be impacted by future climate change. This warming is the result of the thermohaline circulation (THC), driven by global density gradients created by surface heat (thermo) and freshwater fluxes (haline). Variation in the THC could have a dramatic cooling influence in the North Atlantic as climate change impacts both heat and freshwater flux. As far as I am aware though it is not currently possible to measure and model the interactions accurately enough to make confident predictions about the likelihood of the THC being significantly impacted as a result of climate change.

I think this is an interesting chart as it illustrates just how exceptionally warm the North Atlantic and northwestern Europe are for their latitude. The UK for example sits between 50 and 60 degrees North. Within that band we also find the southern tip of Greenland, Vancouver (home of the 2010 winter Olympics), Moscow and the chilly waters of Hudson Bay and the Gulf of Alaska.

Sea level rise is one of the most serious consequences of climate change. This is largely due to the fact that large concentrations of people live on the coast, approximately at sea level. There is also a public communication issue here as the science talks of mm per year. It’s hard to get excited about 3.1 mm/yr (1993-2003, IPCC) when tides move metres in hours. The current rate is probably closer to 4 mm/yr given the acceleration in ice-sheet melt since then. Instead of being scientific, let’s be dramatic, let’s look at London today.

It’s actually Sunday afternoon on the 31st January 2010. I happened to be in Putney on the banks of the river Thames and was surprised to watch the river come over its banks and flood the nearby road. By the look of the parked and flooded cars I wasn’t the only surprised onlooker that afternoon.

I managed to take a few photos on my phone. The photos were taken between 15:08 and 15:12, high tide was officially 15:16 in Putney that day so this was pretty much it. A Putney tide table is available here: http://tides.rjen.me.uk/

The site contains a tide table for Putney Bridge, just a few hundred metres from where the photos were taken (visible in the second shot). The table says the projected high tide height was 7.4 m, certainly a high tide but the projection for the following day was 7.5 m and scanning down the table every ~28 days high tides exceed seven metres for a few days at a time. I don’t believe this high tide was contributed to by particularly strong easterly winds, low air pressure or high proceeding precipitation in the Thames catchment area. This is normal, London and its millions of inhabitants live at sea level. There isn’t much margin to accommodate the potential 1 m (or possible as much as 2 m) sea level rise the science is indicating could occur by 2100, 90 years from now.

The only point to keep in mind is that this road, The Embankment, is the ‘wrong’ side of what flood defences do exist. In some ways it could be said to give a more accurate impression of how vulnerable London is. Were it not for the hard engineered flood defences many more roads would regularly look like this. The map at the bottom of the page is from the Environment Agency (click here for dynamic version). It shows these hard defences in pink and the areas at risk of flooding without defences.

The long term view, several hundred years, could easily see sea level rise of several meters. At which point cities on tidal estuaries like the Thames are unlikely to be viable. What should one do today, if one believes much of London to be uninhabitable in several hundred years time? How much should be invested to protect the city for the next hundred or two hundred years, if its loss four hundred years from now is inevitable? Of course these numbers are just educated guesses but the question is a serious one.

London flood map from the UK Environment Agency

Last week, the Royal Society held a public lecture entitled ‘Geoengineering the climate: A brave new world?’, following their September 2009 publication ‘Geoengineering the climate: Science, governance and uncertainty’. The lecture panelists, like the authors of last year’s publication, were from a wide range of disciplines, reflecting the diversity of issues which arise from geoengineering proposals.

Geoengineering solutions for combating global warming fall into two broad categories. The first, Carbon Dioxide Removal (CDR), addresses the principal cause of climate change by removing CO2 from the atmosphere, and so reducing the greenhouse effect. The second, Solar Radiation Management (SRM), involves countering the warming effects of high atmospheric CO2 by reflecting some of the radiation from the sun.

Examples of suggested CDR techniques include biochar; aforestation; ocean fertilisation; and enhancement of weathering. SRM methods include increasing the albedo of the earth, such as by painting building roofs white; increasing the reflection of radiation from the stratosphere by releasing aerosols; and space-based methods which reduce the amount of radiation reaching the earth, such as by launching reflectors into space.

The immediate benefit of CDR over SRM is that it removes CO2 and so would counter ocean acidification (and other CO2-related problems), whereas SRM only prevents warming. However, some methods for SRM could be deployed very rapidly, most CDR methods would take years or decades to become effective.

The only panelist who opposed any further research into geoengineering was Greenpeace senior scientist Dr. David Santillo. The opinion of Greenpeace, and of many other opponents, is that focussing on geoengineering solutions to the climate problem diverts attention (and funds) from what is sometimes termed ‘Plan A’: the reduction of CO2 emissions. The possibility of a ‘Plan B’ may be regarded by governments, industry and the public as an excuse to continue burning all remaining fossil fuel reserves. An uncertain cure in the place of a more reliable prevention.

However, it can not be assumed that all serious advocates of climate geoengineering see it as an alternative to emissions reduction, but rather as a necessary additional measure. This is the logical conclusion from the increasingly popular view that present levels of atmospheric CO2 are already so high that certain tipping points in the earth climate system have been reached (most recently). This position asserts that even if emissions fall to zero tomorrow, ‘catastrophic climate change’ is still probable.

The problems with geoengineering are wide-ranging and hard to predict, but stem from three main areas:

Firstly, designing successful methods to reduce either atmospheric CO2 levels, or solar radiation absorption require an excellent understanding of the earth system. At the Royal Society, Professor Corinne Le Quéré, from the University of East Anglia, reminded us that current models are still not accurately reproducing observation in a number of fields, Arctic ice melt, for example.

Secondly, implementation of the technology itself could prove prohibitively expensive. This is certainly the case with space-based SRM methods. As well as monetary costs, implementation of some technologies may be expensive in terms of space and resources. Aforestation, for instance, risks competing for fertile land with agriculture.

Thirdly, and perhaps most critically, major geoengineering projects would require international cooperation. Although some CDR techniques, such as biochar and land use changes, could be applied in specific areas, without need for consent from others, they would actually need to be implemented across large areas of the world to be effective. Certain SRM techniques, however, could be carried out by one country (perhaps by releasing aerosols into the stratosphere), and would be effective over the entire globe. This category of technique could be damaging to the climates of certain parts of the world, for example by reducing precipitation. Added to this is the fact that once a particular SRM is started, it will have to continue indefinitely. If suddenly terminated, rapid warming would commence, with disastrous consequences. After the recent failure of world leaders to agree upon emission reductions at Copenhagen, how can we rely upon them to reach an agreement over the much more complex issue of geoengineering?

Plan A may have already failed, plan B is not a silver bullet solution, which leads me to consider plan C: Adaptation. Millions, perhaps billions of people are at risk of being displaced by sea level rise, drought, famine and other effects of climate change. Humankind has adapted to changes in climate before, by migrating, by changes in behaviour, and by inventing new technologies. With a population of nearly seven billion, the task is certainly tougher this time. But perhaps it’s the most feasible option left to us.