In 1990, Yale economist William Nordhaus wrote an article titled “Count Before You Leap” in which he warned of the consequences of 'doing too much to prevent climate change, given uncertainties about both the effects of climate change and the likelihood that those effects will actually occur. Nordhaus advocated a careful cost-benefit analysis based on more reliable information about climate change rather than a knee-jerk reaction to dark prophecies about the end of the world as we know it. He argued that very little economic activity in industrialized societies is climate dependent and that significant losses of GNP would likely be incurred in an effort to mitigate climate change. According to him, “a vague premonition of a potential future disaster is not a sufficient reason to plunge the world into depression. But if scientists can identify the likelihood of catastrophic risks, then citizens and governments can rationally decide how much "climate insurance" to purchase. So, according to Nordhaus, what was known about climate change merited further research, but it hardly justified aggressive action to prevent the possibility of climate change. There is a lot of pressure on climate scientists to be certain about their theories because of the way politics is done (Norgaard). Policymakers must allocate money so that the costs of a given policy are justified by the benefits, and climate change mitigation is one agenda item on hundreds of different issues . Estimates of the cost of reducing CO2 to neutralize the effects of climate change vary from $10/tonne of reduced CO2 to $250/tonne (Norgaard). Given such a wide range of estimates, it is understandable that policymakers demand certain CO2 levels, because by then it will already be too late to avoid certain unacceptable consequences. . Since the consequences of waiting could cause serious or irreversible harm to the public, in the absence of clear scientific data on what exactly will happen, the burden of proof falls on those advocating waiting. Let them prove that we must wait. In the meantime, we must act on what we already know and move aggressively toward climate change mitigation and prevention policy. Hansen, James et al. “Targeting atmospheric CO2: where should humanity aim?” » Washington DC: NASA, 2007.2. Hansen, James. “Why we can’t wait.” The nation. May 7, 2007.3. Nordhaus, William D. “Count Before You Leap.” » The Economist July 7, 1990.4. Norgaard, Richard. Conference. ERG 280. Cory Hall, UC Berkeley, Berkeley, CA. March 11 2008.