23 May 2009
In 1996 the United Nations Intergovernmental Panel on Climate Change’s (IPCC) Second Assessment Report was released, and I was listed as one of approximately 3000 “scientists” who agreed that there was a discernable human influence on climate.
I was an invited reviewer for a chapter dealing with the economic impact of sea level rise on small island nations. In keeping with IPCC procedures, the chapter was written and reviewed in isolation from the rest of the report, and I had no input into the process after my review of the chapter draft. I was not asked if I supported the view expressed in my name, and my understanding at the time was that no evidence of a discernable human influence on global climate existed.
The chapter I reviewed dealt primarily with the economic consequences of an assumed sea level rise of 1 m causing extensive inundation. My response was that I could not comment on the economic analysis, however, I disagreed with the initial assumptions, particularly the assumed sea level rise in the stated time period. Further, there was good evidence at the time that sea level rise would not necessarily result in flooding of small island nations, because natural processes on coral atolls were likely to raise island levels.
The IPCC Second Assessment Report assessed sea level rise by AD 2100 as being in the range 0.20-0.86 m, with a most likely value of 0.49 m (less than half the rate assumed for the economic analysis). Subsequent research has demonstrated that coral atolls and associated islands are likely to increase in elevation as sea level rises. Hence, the assumptions were invalid, and I was convinced that IPCC projections were unrealistic and exaggerated the problem.
Following the release of IPCC Second Assessment Report I also co-authored the sea level rise section of the New Zealand impact report, and same section for a revised report following the release of IPCC Third Assessment Report (2001). The third report followed the trend of decreasing sea level rise projections evident in sea level rise literature, with a most likely projection of 0.44 m. However, some extreme scenarios were added at a late stage of the review process to give a wider range of projections from 0.09-0.88 m. There was little support in the literature for these extremes, and my view was that a range of 0.31-0.49 m was more reasonable. I also expected future projections to be lower.
For the New Zealand 2001 report, I was asked to state that sea level rise was accelerating, or at least could be accelerating. However, my own research and published literature shows that sea level fluctuates at decadal time scales. Therefore, although there was an increase in the rate of sea level rise around 1998, I expected sea level rise to slow and reverse early in the 21st Century. The underlying long-term trend, however, was likely to decrease, and there were some tide gauge data to indicate that it had started to do so. In the 1980s, the New Zealand rate was 1.8 mm per year. By 1990, it was 1.7 mm per year, and by 2001 it was 1.6 mm per year. These changes are small, and were not enough to prove that sea level rise was slowing. However, they clearly did not show that sea level rise was accelerating.
After 2001, published studies continued to project lower global sea level rises over the 21stCentury, and several reported a slowing of the rate of rise during the 20th Century. Shortly before the IPCC Assessment Report 4 was published I undertook a literature review of all sea level studies, which: projected lower levels than the IPCC Third Assessment Report review; indicated a slowing of the rate of sea level rise; emphasised the role of decadal scale fluctuations; and there was concern about the discrepancy between satellite and tide gauge sea level measurements. It was recognised that, although satellite sensing gives a better overall measurement of global sea level, satellites reported twice the rate of sea level rise being measured at the coast. It was evident that satellite data could not be combined with tide gauge data.
The IPCC Assessment Report 4 report emphasises a single paper, which was not available when I conducted my review, which spliced the satellite data onto the tide gauge data to “find” acceleration in sea level rise over the period of satellite measurement. This is being used to imply that global sea level rise is accelerating due to global warming (now renamedClimate Change). The satellite data only covered the period of increasing sea level associated with decadal cycles, and the known discrepancy between satellite trends and tide gauge trends was not corrected for. This is poor science comparable to the splicing of proxy and instrument data in the infamous Hockey Stick graph, and the splicing of ice core and instrumental CO2 measurements to exaggerate the changes.
Despite therefore finding accelerating sea level rise, the latest IPCC assessment projects lower sea level rises than the previous ones. The methodology used to report the projections was changed to make comparisons harder, but the range of 0.18-0.59 m equates to a most likely rise of around 0.39 m. The IPCC Assessment Report 4 also included an extra 0.20 m allowance for uncertainties associated with destabilisation of the Greenland and West Antarctic Ice Caps. Various groups have speculated that the collapse of these Ice Caps could produce a much higher additional sea level rise. In contrast, published studies that have specifically studied this contribution have concluded that given the worst possible scenarios, the maximum extra contribution is 0.18 m. Hence, the IPCC Assessment Report 4 allowance is a very conservative upper bound.
What has sea level actually done so far this century? There have been large regional variations, but the global rate has slowed and is currently negative, consistent with measured ocean cooling. Claims to the contrary are exaggerations and not realistic.
So, given my understanding of oceanography, what do I believe about climate change? Firstly climate change is real, and has occurred on Earth for at least 4 billion years – as long as an atmosphere and oceans have existed. Climate change occurs in cycles at various time scales, with the shorter time scales known as weather (by convention the distinction is 35 years). Trying to stop or control climate change is akin to stopping ocean tides. Secondly, I believe human activities affect climate, otherwise why would I bother with a mortgage. The climate inside my house is different to the climate that would exist if my house were gone.
There are many ways human activities affect climate on a small scale. Interestingly the concentration of CO2 is not one of them (CO2 are often elevated inside buildings). As the size of the area considered increases, the impact of human activities decreases. As the latest IPCC report notes, there is no convincing evidence of the impact of CO2 (or any other human influence on climate) at a continental scale. Yet, they say that the impact of a CO2 (and other gases treated as effective CO2) is the dominant driver of climate at a global scale and will have catastrophic consequences. This conclusion I strongly disagree with. Why?
It is frequently pointed out that the Earth is approximately 32°C warmer than it would be without an atmosphere due to the Greenhouse Effect. This is misleading, as the climate system responsible for this extra warmth includes many components. Important ones omitted in most discussions are clouds and oceans. About 70 percent of the Earth’s surface is covered in water, which absorbs sunlight and warms up. The oceans retain heat better than land, and, while slow to warm up, they cool slowly and warm the surroundings (a maritime climate).
Considering the available data, it is clear that the oceans warmed over the 20th Century by about the same amount as the atmosphere. This agreement should not be entirely surprising as 70 percent of the mean global air temperature comes from over oceans. The inconvenient truth that is generally ignored, is that the atmosphere is not capable of warming the oceans to any significant degree – 99.9 percent of ocean heat is derived from sunlight at wavelengths less than 3 microns. The balance is mostly from heat leaking from the interior of the Earth. The Greenhouse Effect involves a delay in the loss of infra-red radiation at wavelengths greater than 5 microns.
What does this mean for climate change? It means that variations in the amount of sunlight reaching the oceans will control the rate at which the oceans warm. This is influenced at long time scales by changes in the Earth’s orbit. At short time scales there are changes in the amount of sunlight associated with the sunspot cycle. These changes are small, but due to the ability of the oceans to store heat it may be possible to have a cumulative effect as sunspot cycles wax and wane. However, the main control is the amount of cloud and ice cover. Clouds and sea ice reflect sunlight before it can be absorbed by the oceans, and is referred to as albedo. Albedo changes have a greater influence on climate than the Greenhouse Effect, and are usually invoked to produce the catastrophic consequences of “Climate Change” (aka Accelerated Global Warming).
Oceans lose heat through evaporation (53 percent), infra-red radiation (41 percent) and conduction (6 percent). The Greenhouse Effect can slow the loss of the infra-red radiation, thereby warming the atmosphere but not the oceans. However, evaporation accounts for more than half the heat loss. Evaporation produces clouds, and hence there is a feedback loop – warming the oceans results in more evaporation, producing more clouds, which increases albedo, which cools the oceans. This is exactly what was observed during The Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE) that was set up to investigate the Pacific Warm Pool – the warmest ocean water in the western equatorial Pacific Ocean. COARE also found that rainfall would cool the ocean surface, so increased evaporation producing rain is another feedback loop.
What does this have to do with the 20th Century? Well the observed climate change is consistent with variations in albedo and associated ocean warming and cooling, suggesting that it is just a natural cycle. This pattern of behaviour is evident in palaeoclimate data for most of the last 10,000 years. None of this is simulated in climate models. Instead they focus on the 20th Century increase in CO2, CH4 and a few other greenhouse gases. The increasing concentrations correlate well with global temperature. This is taken as proof that the greenhouse effect is driving temperature.
However, it is also correct that changing ocean temperatures affect the concentration of these gases in the atmosphere. At annual and 2-7 year time scales it is clear that the concentration of CO2 in the atmosphere is strongly driven by the ocean. At longer time scales it is also clear that the concentration of greenhouse gases lags behind, and therefore is driven by, temperature. Once again the oceans are the likely control on atmospheric greenhouse gas concentrations. The IPCC position requires that for 50-100 year periods everything works in reverse, which still showing an oceanic influence at shorter timeperiods. It is more likely that the warming of the oceans since the Little Ice Age is a major contributor to the observed increase in CO2. Carbon isotopic ratios indicate that while there is a contribution from the burning of fossil fuels, it is of the order 1-5 percent of the increase.
So, I am a climate realist because the available evidence indicates that climate change is predominantly, if not entirely, natural. It occurs mostly in response to variations in solar heating of the oceans, and the consequences this has for the rest of the Earth’s climate system. There is no evidence to support the hypothesis runaway catastrophic climate change due to human activities.
Posts
