Validate and verify
Last week, presidents of the 18 prominent American scientific societies wrote Senators a letter making it clear climate change is occurring and that greenhouse gases emitted by human activities are the primary cause. They noted the strong evidence that ongoing climate change will have broad and severe impacts on society, the global economy and the environment that can only be avoided by dramatically reducing emissions of these gases.
This will require reducing emissions of CO2 from burning of fossil fuels through conservation and switching to renewable sources of energy. Stopping leaks of methane-containing natural gas will also help. Improved management of land-use changes (currently estimated to contribute 18% of global CO2 emissions), farming practices, and other activities that can either release or consume and sequester greenhouse gases should also contribute to the needed emission reductions. However, to be truly effective such offsets must be additional to activities being pursued anyway, sequester carbon more or less permanently, and account for any increased emissions that indirectly result from the practice, for example if expanded biofuels production causes deforestation. This places a heavy requirement for fully validating the effectiveness of the offset and verifying that it has been applied completely in order to ensure results and avoid abuse of the system.
We cannot rely totally on such offsets to achieve the needed reductions in emissions, which must come predominantly from reducing the primary emissions. Still, practices that additionally lower net emissions of greenhouse gases (and have other co-benefits, such as reforestation) and stabilize atmospheric concentrations will have to be aggressively pursued under either cap-and-trade or carbon tax regimes. But they should not be blithely trusted and must be verified.
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