Saturday, April 07, 2007

Global heating & ecosystem responses

The IPCC 4th Assessment Report, Climate Change 2007, Summary for Policymakers: Climate Change Impacts, Adaptation and Vulnerability was released last night. The earlier IPCC report on the science of warming came up with forecast temperature rises to the end of this century of between 1.1-6.4 degrees C with a best guess range from 1.8-5.4 degrees C with a midpoint of 3,6 degrees C. The latest report looks at ecosystem responses.

Despite the sensationalist responses in parts of today's press (The Australian outdid itself by mixing up reports from the IPCC with comments to the press by IPCC members, leaving out almost all qualifiers) the IPCC report itself seems to me serious but moderate.

Anthropogenic warming is impacting on physical and biological systems. The effects will be mixed across regions for temperature increases of up to 3 degrees C but low latitude and Polar Regions will be severely impacted on by even small temperature increases.

The appraisal draws on improved data covering the period post-1970 though most of these studies cover developed, Northern hemisphere countries. There are comparatively few studies in South America, Australia-New Zealand and Africa though there is a concentration of studies in Antarctica. Globally, of more than 29,000 observed data series from 75 studies showing changes in physical and biological systems more than 89% are consistent with the direction of change expected as a consequence of warming - natural variability is unlikely to account for observed effects. Moreover, models with combined natural and anthropogenic forcings simulate responses better than those with natural forcing alone.

The main findings are that, in response to global warming:

With ‘high confidence’ (8 out of 10 chance), natural snow ice and frozen systems are being affected. Glacial lakes are increasing in size and number with increasing ground instability in permafrost regions and rock avalanches in mountain regions. Arctic and Antarctic ecosystems are being affected including those in sea-ice biomes and also predators high in the food chain.

With ‘high confidence’ hydrological systems are being affected with increased runoff and earlier spring-peak discharges in many glacier and snow-fed rivers.

With ‘very high confidence’ (at least 9 out of 10 chance) based on additional evidence from a wider range of species than surveyed in IPCC 3, terrestrial biological systems are being affected. Spring time leaf unfolding, bird migration and egg-laying are occurring earlier and there are poleward and upward shifts in plant and animal species. Plants are greening earlier in the spring with longer thermal growing seasons.

There is ‘high confidence’ that changes in marine and freshwater biological systems are occurring in response to changed water temperature, changes in ice cover, salinity and oxygen levels and circulation. The uptake of anthropogenic carbon has made the oceans more acidic though the implications of this are unclear – this should affect marine shell-forming organisms such as coral reefs.

Other effects on agriculture and forestry in Northern hemisphere higher latitudes (earlier crop planting, forest fires and pests), heat related mortality in Europe, infectious diseases and allergic pollen effects are being observed in the Northern hemisphere and attributed to temperature increases with medium confidence.

Other effects such as increased risks to mountain settlement due to glacier floods, warmer and drier conditions in Africa and losses of coastal wetlands and increased damage from coastal flooding are being observed but, as yet, do not constitute clear trends.

Among the impacts of relevance to Australia:

A 20-30% decrease in river runoff and water availability in water-stressed areas. An increase in the extent of drought affected areas and an increased frequency of high precipitation events triggering flooding.

Ecosystem resilience exceeded by an unprecedented combination of climatic change, associated disturbances (flooding, drought, wildfire, insect, ocean acidification) and other anthropogenic changes related to changed land use.

Net carbon intake by terrestrial ecosystems will peak before mid-century and then reverse amplifying effects of climate change.

20-30% species extinctions if increases in global average temperatures exceed 1.5-2.5 degrees C as seem plausible given the earlier IPCC report.

Agricultural prioductivities will increase slightly for local mean temperature increases of 1-3 degrees C and then decrease beyond that in some regions. In dry and tropical regions at lower latitudes productivities should fall. Globally food production should increase with temperature increases in the range 1-3 degrees C but decrease beyond that.

Effective agricultural adaptations include use of altered cultivars and changed growing seasons.

Coastal zones will be exposed to increased risks including coastal erosion. Coals are vulnerable to thermal stress and have low adaptive capacity. Coastal wetlands will be adversely affected particularly when they are constrained on their landward side and starved of sediment.

Among the health effects will be increased frequency of cardiovascular diseases due to higher concentrations of ground level ozone. There will also be changes in the distribution of infectious diseases. In temperate areas health will improve through lower levels of cold exposure.

Many of the most severe effects are concentrated in developing countries. In terms of specific impacts on Australia:

As a result of reduced precipitation and increased evaporation, water security problems are projected to intensify by 2030 in southern and eastern Australia.

Significant loss of biodiversity is projected to occur by 2020 in some ecologically-rich sites including the Great Barrier Reef and Queensland Wet Tropics. Other sites at risk include Kakadu wetlands, south-west Australia, sub-Antarctic islands and in alpine areas.

Ongoing coastal development and population growth in areas such as Cairns and Southeast Queensland are projected to exacerbate risks from sea-level rise and increases in the severity and frequency of storms and coastal flooding by 2050.

Production from agriculture and forestry by 2030 is projected to decline over much of southern and eastern Australia due to increased drought and fire.

Australia has substantial adaptive capacity due to its well-developed economy and scientific and technical capabilities, but there are considerable constraints to implementation and major challenges from changes in extreme events. Natural systems have limited adaptive capacity.

Water management strategies in Australia are singled out as important adaptation measures. These will complement mitigation strategies in reducing the risks of climate change.

This picture of likely trends in Australia is more specific with respect to rainfall forecasts than earlier CSIRO discussions but still non-specific. The earlier forecasts provided almost no specific forecasts on likely future rainfall patterns – I am not suggesting this is easy – but then link agricultural outcomes to forecast rainfall effects. This is unhelpful. Hopefully the CSIRO who have provided much information to the IPCC will now provide detailed forecasts to resident Australians.

Some work on the effects of climate change on marine environments was released this week – the executive summary is here and the arguments reviewed here. Kevin Hennessy (a CSIRO scientist who is part of the IPCC team) made more specific predictions in a media release after the release of the IPCC report including forecasts of a 10-25 per cent reduction in runoff in the Murray Darling Basin by 2050. Geoff Love, another climate change expert and IPCC member, made specific forecasts that the Great Barrier Reef would be destroyed if temperatures rose 3 degrees C.

These specific forecasts are news to me – they are not part of the IPCC Summary document and I will follow them up.

The observations about endangered biodiversity sites are well-known. Observations on coastal development and agriculture seem new.

Final Asides

There remain extraordinarily high levels of uncertainty about the discounted social costs of emitting a tonne of carbon. The average figure is $12US per tonne of CO2 but the range of estimates examined vary from $3-$130 per tonne of CO2! This range depends on different assumptions regarding climate sensitivity, different assumed response lags, different treatments of risk and equity, the inclusion or not of catastrophic losses and the choice of discount rate.

Climate change blogs have been slow to react to the report but Climate Ark wrote a fairly hysterical piece emphasizing that the final report had the views of scientists extensively modified by politicians. How exactly would one expect the UN to react? I’ll add further links as they become available.

4 comments:

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shooflypie said...

Don't know about you, but I'm scared :(
Found a html version of the IPCC report at http://www.unregisterednews.com/content/view/120/51/

Bruce said...

Harry this seems to me to be a long list of relatively minor and highly speculative points.

For a start, where or when in Australia has there ever been a Spring season? I've never known weather stability in my 50 plus years in Australia, and only two very roughly distinct seasons overall - hot and cold. Yet it seems that is the implicit base assumption for the whole report, 'all other things being equal', which they never were and never will be.

The early settlers in Sydney drew pictures of icebergs floating past the Heads. I think we've already experienced much worse weather extremes than anything in that list.

Is that all you've got?

hc said...

Bruce, Its not me - its the IPCC. I have posted on other sites that their reaction to this report has been a bit hysterical - most of the issues have been well-established since 2001 by CSIRO.

I guess the forecast temperature range is wide and the rainfall forecasts are very, very uncertain so it is difficult to come up with anything other than very speculative forecasts.

Warming is having an impact but you are right - the impacts are speculative and uncertain.