Climate compendium: important insights

By Bryan Walker 28/09/2009

Compendium’The Climate Change Science Compendium is a wake-up call. The time for hesitation is over’. So wrote Ban Ki-moon in his foreword to this UN Environment Programme publication released last week. The publication is a review of how climate science has evolved since the Fourth Assessment Report (AR4), and is based on some 400 major scientific contributions in the peer-reviewed literature or from research institutions since the deadline for inclusion in AR4 three years ago. It appears in response to the request of many governments and stakeholders for a snapshot update. Achim Steiner, the Executive Director of the Environment Programme makes it very clear that it doesn’t replace the painstaking rigour of an IPCC process, but he hopes it will provide important insights into the rapidly developing and fast moving realm of climate science so that the choices made by leaders in Copenhagen in December are informed by the best and the latest research available to the international community.

His hopes are well justified. It’s unquestionably an important document. Whether it will be read and absorbed by policy makers is another question, but I can attest that you don’t need to be a scientist to follow it and it leaves policy makers without excuse if they claim they didn’t realise how fast things were moving.

I’ve selected one of the five chapters, on Earth’s ecosystems, to give an idea of how the document presents its findings.

The compendium reports the recent work of researchers by threading frequent reference to their papers into an organised narrative.  This chapter in general terms notes that for both marine and terrestrial ecosystems, the most challenging irreversible climate-related changes include altered chemical characteristics of the ambient environment, inundation of many small islands and low-lying coastal ecosystems by sea-level rise, loss of wetland quantity and quality, and increased aridity in sub-tropical areas. It is these changes and their cumulative effects, proceeding at unprecedented rates, which will profoundly alter ecosystems and result in widespread species extinction. Since the closing date for submissions to the AR4, wide-ranging surveys and analyses suggest that such changes are occurring in all well-studied marine, freshwater, and terrestrial groups. Analysis has been used to eliminate factors such as land-use change, management practices and pollution, leaving robust evidence of anthropogenic climate change as a major cause.

In looking at marine ecosystems in more detail the compendium reports both observations and projections of the effects felt by marine species. A recent study, for example, suggests numerous local extinctions will have occurred by 2050 in ecosystems in subpolar regions, the tropics, and semi-enclosed seas. Conversely the Arctic and Southern Oceans will experience severe species invasions. All told there may be a dramatic species turnover of up to 60 percent.

Ocean acidification studies are reported, with concerns emerging that it may not only result in reduced calcification in coral reefs and other calcareous organisms but also impose a physiological strain on marine animals, impairing their performance and reducing their energy.

In coastal regions increasing extreme events are likely to impact on ecological dynamics and ecosystem functioning.  The tremendous ecological value of mangroves and their rapid degradation rates has been the subject of a number of studies. One study reports how sea level rise presents an imminent threat to freshwater-dependent ecosystems on small oceanic islands.

Moving to terrestrial ecosystems the compendium notes studies pointing to ecosystems committed to long-term change long before any response is observable.

One study, using climate projections based on a relatively low greenhouse-gas emissions scenario, predicted the local loss of at least 10 percent of the vertebrate fauna over much of North and South America, with much larger, over 90 percent, species change for the tundra, Central America, and the Andes Mountains.

Disappearing and novel climates spell ecological changes, since climate is a primary control on species distribution and ecosystem processes. Novel climates are projected to develop primarily in the tropics and subtropics, whereas disappearing climates are concentrated in tropical montane regions and the poleward portions of continents. The complexities of effects on ecosystems are all too apparent, as are the demands they place on ecosystem management. Attempted restoration in what have become essentially novel systems has to be examined closely.

The expansion of the tropical belt and the poleward displacement of the subtropical zones occupied by most of the world’s deserts has a cascading effect on precipitation patterns that determine natural ecosystems, agricultural productivities, and water resources. Shortages of water for agriculture and for basic human needs are threatening communities around the world as evidenced by southeastern Australia and southwestern North America.

The compendium proceeds with reports on studies of a number of regions. The uncertainties of future precipitation patterns in the Sahel, the likelihood of more severe aridity in the Mediterranean than previously estimated, the likelihood of drought becoming the region’s new climatology in southwestern North America, the creeping threat of climate change such as decreased dry season precipitation in the Amazon, the thawing permafrost and increased plant growth in the permafrost areas of the Arctic, the rapid shifts in plant distribution in mountains.

A final section on ecosystem adaptation points to the need to consider multiple interactions and feedbacks, and discusses strategies which have ecological and societal benefits.  The strategies include greenhouse gas reductions primarily in industrialised nations, reduced desertification in arid zones, and reduced deforestation in the tropics.

There’s little in the chapter that anyone following the subject won’t have seen mentioned somewhere in recent times. But the value of the compendium is that it gathers scattered material into a coherent narrative and sources it to the relevant research papers which have informed it. There’s a great deal of scientific work being done and it’s all pointing in the same general direction. Much more will be needed to help us cope with what lies ahead, but there’s already quite enough to declare serious danger.