26 Aug 2010

5 questions on climate change

I recently covered the U.S. National Oceanic and Atmospheric Administration (NOAA)'s 10 answers to allegations that 'Climategate' disproves warming- see here. Well below is a bit more info that was largely put together by a Green party colleague to the five most common claims regarding our climate. I cover this issue again as I just had another conversation with someone who raised two of these questions with me. Some of these typical points have now been repeated so widely that
they are becoming accepted as fact and often go unchallenged, right
through the national media, even on the BBC.

Also just read 17 countries experience record temperatures; 2010 sees record highs in Russia, Belarus and Ukraine but also many African, Middle Eastern and Latin American countries. Anyway...

Photo: another poster produced by those disputing climate change

1. Climate changed peaked in 1998 and the world has been cooling since. Why is this happening when CO2 is still rising relentlessly?

2. Solar activity caused the warming.

3. The polar ice cap has recovered all its recently lost area.

4. Sea level is not rising.

5. The cold winter of 2009/10 in the UK and Europe disproves global warming.


1. Climate changed peaked in 1998 and the world has been cooling since. Why is this happening when CO2 is still rising relentlessly?

1998 was an exceptionally warm year (global average) but several years in the 2000s were very similar, within the accepted margin of error of the measurements (ie about 0.1 C). It is true that since the late 1990s, the warming curve has flattened out, but it is totally untrue that global average temperatures have fallen back. Overall the 2000s were warmer than the 1990s showing that the decadal mean is still rising (UK Met Office). The sceptics do accept that CO2 levels are rising but try to de-link this with global warming. They fail to understand that the temperature curve will not exactly match the CO2 curve year to year (see 2 below). (Temperature data source NASA GISS).

2. Solar activity caused the warming.

The Sun, volcanic activity, changes in ocean currents, etc, etc, are all factors that must be taken into account when analysing past data and when trying to model future climate. The radiation received from the Sun can be accurately measured. Observed solar variability is not enough to explain observed global warming and in any case, total solar irradiance peaked about 1960 and has been marginally lower since - it does not fit the temperature curve. In the second half of the 2000s there has been a deep solar minimum and corresponding measurable drop in solar irradiance. It is possible that this has been a cause of the global warming trend flattening in the 2000s.

3. The polar ice cap has recovered all its recently lost area.

The northern polar ice cap has been consistently retreating (over and above the annual waxing and waning) over several decades and the area of sea ice has now been at (very briefly) or well below (most of the time) the long term average every month since early 2003 (Cryosphere Today; U. of Illinois). In late 2007 the summer melt reached over 2.5 million km2 below average. The curve has shown signs of flattening in the last few years, which is consistent with 1 and 2 above, but it is simply untrue that the ice area has recovered in the arctic. There is also evidence that the ice is thinning, as well as the area reducing.

For reasons that are not clear yet, antarctic sea ice is not retreating as it is in the arctic.

4. Sea level is not rising.

Sea level is rising as measured at tide gauges and by satellite.

5. The cold winter of 2009/10 in the UK and Europe disproves global warming.

The UK has just experienced its coldest winter probably since 1978/9 and northern Europe and large parts of Russia have also been very cold. Globally, January/February 2010 was the 3rd warmest in 131 years (NASA GISS). Whilst Europe froze, unsually warm conditions were prevalent over much of the rest of the planet with very high positive temperature anomalies over Canada and much of the arctic. Most of South America and Africa were also warm. The Middle East had a very warm winter. The fact that the UK had a cold winter does not disprove global warming because (a) the UK is a tiny part of the Earth's surface and (b) because such comments fail to distinguish between weather (short terms variations) and climate (30 years averages). Climate change does not mean that every year globally or locally will be warmer than the last. See my blog earlier this year "Weather is not climate".

Here is a last comment from my colleague:

As a final point we should add that good science is about keeping an open mind and seeking good evidence. We cannot say that it is 100% certain that the climate change science is completely correct and nor should we. However, the probability that it is correct is high and the actual observations do not suggest there is any significant error in the science. Sceptics will continue to try and cherry pick "facts" to try and undermine the science and in doing so confuse weather with climate, fail to understand the large number of factors that cause climate variations and fail to understand that climate change is a long term trend, not a sudden lurch (although there are triggers that could cause sudden change).

The bottom line is that the atmospheric concentration of CO2, the chief global warming gas we are changing, is rising relentlessly (now 40% above pre-industrial levels) and it would be one of the biggest science shocks of all time if that and predicted much higher levels of CO2 concentration had little or no warming effect as the sceptics claim.

1 comment:

Philip Booth said...

I just got this from a friend:

I saw this on your blog, and remembered that I had seen an explanation on the astronomy forum...with link to National Geographic article.


"Climate scientists have cracked the mystery of why Antarctic sea ice has managed to grow despite global warming—but the results suggest the trend may rapidly reverse, a new study says.

Satellite data show that, over the past 30 years, Arctic sea ice has declined while Antarctic sea ice has mysteriously expanded, according to study leader Jiping Liu, a research scientist at Georgia Tech in Atlanta.

"We've seen this paradox, but we don't know why—here we gave an explanation," Liu said.

The new analyses are based on climate models and sea-surface temperature and precipitation observations from 1950 to 2009. They show that, in the 20th century, ocean warming boosted precipitation in the upper atmosphere over the Antarctic region, which fell as snow.

More snow made the top layers of the ocean less salty and thus less dense. These layers became more stable, preventing warm, density-driven currents in the deep ocean from rising and melting sea ice."