Image for The terrible consequences of deforestation

Bob Burton’s article posted on TT HERE: Who’d Pay for Rupert Murdoch’s Climate Change Skepticism? raises the subject of the role of water vapour in climate change.  Other TT discussions have canvassed the REDD (Reducing Emissions from Deforestation and Degradation) proposals from Copenhagen.  I would like to extend these discussions.

Some time ago, while researching climate change, water and land use policies as a political candidate, I came across an interesting article on this web site: HERE

“We believe if there is climate change - which is manifested regionally and consists of three only indirectly related phenomena; drought, extreme weather, and global warming - it is the result of deforestation far more than the result of human CO2 emissions. And with respect to deforestation and sea level rise, it is clear that deforestation, at least theoretically, has had a far more dramatic impact on sea level rise than construction of large reservoirs.

There is an extremely interesting website called “Ten Billion Acres,” (HERE) that advocates “reforesting planet earth for the sake of human survival.” They take the position, with detailed arguments that are at the very least thought provoking, that “were there enough Trees in the equation, Climate Change would not be occurring other than that which would be normal for the Earth’s and Oceans’ cycles during this Era.” “Ten Billion Acres” refers to the amount of deforestation experienced on earth in the last 500 years - accelerated in the last 150 years. We’ve verified these numbers - ten billion acres is approximately 15 million square miles or 40 million square kilometers - so how much land-based water was lost when these trees were cut down?

It is shockingly difficult to get online data on the water content of trees, but thanks to Google Books, there is a 1896 study available that documents the water content of a variety of representative species of trees through the cycle of seasons. The study is entitled “On the variation of water content in trees,”  HERE by James Barkley Pollock of the University of Wisconson. And it is clear from the data presented that the water content of trees is at least 50%, averaged across all trees and all seasons.

If you assume, for a global average, a forest has one tree for every five square meters, and that each tree has 10 cubic meters of mass (you can roll that around, this average assumes a rather dense forest of rather small trees, but overall these are probably somewhat conservative assumptions), then with a 50% water content, land based water that’s been lost to the oceans through deforestation would total 40,000 cubic kilometers, 4x the water volume sequestered in large reservoirs. And this number is grossly understated, since trees also sequester water underground as well as play a crucial role in replenishing aquifers. So why aren’t sea levels much higher?

At the least, these calculations indicate we still understand very little regarding the global hydrologic cycle. The volume of subsurface water, and the impact of depleting these aquifers still requires significant investigations. Our conclusion is that once again, the emphasis on CO2, or reservoirs for that matter, is misplaced. We should be figuring out how to increase forest canopy, particularly in the tropics where deforestation has the most significant impact on rainfall, aquifer health, climate, and global atmospheric quality. And we should be figuring out how to restore positive inflow to every aquifer on earth, where negative drawdowns have been grossly unsustainable ever since the invention of the mechanized pump.”

Other research from Australia suggests that, since European settlement, more than 12 billion trees have been removed from the Murray Darling Basin.  If we allocated an average 2 cubic meters for these trees (and I have no idea whether this is an overestimation or underestimation – can anyone assist?), then the amount of water stored in trees that has been permanently removed from the Basin would be about 12,000 GL. 

For comparison, the total volume of water stored in all of Australia’s large reservoirs is about 80,000GL.  The total water extracted from the Australian environment in 04-05 for irrigated agriculture was about 12,000 GL. The value of production from irrigated agriculture in the Basin for the same period was about $3 billion.  See http://www.water.gov.au

The biochemistry of photosynthesis provides that for every tonne of water stored in a living tree, 2.44 tonnes of carbon dioxide is removed from the atmosphere.  So the 12,000GL of water lost to the Murray Darling in trees also equates to a lost potential of nearly 30 billion tonnes of carbon dioxide.  At $30 per tonne of CO2e in a emissions trading scheme, that is about $900 billion of lost potential – 300 $years worth of agricultural output. 

Tracking these calculations back to the value of the water embodied in the trees, every tonne of green tree embodies about $36 of stored water value.  Historically, we have allocate no value to the water in decisions on log pricing, forestry and land clearing operations.

At last count, the Federal Government has allocated budgets of over $20 billion to various schemes aimed at staving off the water crisis in the Murray Darling Basin.  Add to this the billions estimated to be needed to support programs aimed at reducing carbon emissions.

Putting all this together, surely there must be potential to combine greenhouse, water and land-use policy in Australia.  Could we be using water as a proxy for carbon dioxide?