Estimating the Likely Harms from Global Warming: A Fresh Look at Accounting for Adaptation and Resilience, and Recommendations for a Bottom-Up Approach

We urgently need to determine a reasonable ballpark estimate for the likely harms from global warming before we commit to a set of mitigation policies, because aggressive mitigation of global warming by forcing a quick transition to low-emissions technologies could be very costly and disruptive to human society, while slow action could leave us vulnerable to serious harms from climate change.&nbsp; I attempt here to improve our understanding of the likely harms if we do nothing to reduce global warming.&nbsp; This paper does three things: (1) evaluates the literature on the harms from global warming, and finds it lacking; (2) introduces an alternative framework for analyzing the harms, that incorporates adaptation and resilience, and is based on a bottom-up approach with multiple metrics and types of harms; and (3) provides a very preliminary assessment of the likely harms under a business-as-usual scenario.&nbsp; I provide some new perspectives on the debate, namely that human society has developed a tremendous resilience and ability to adapt to known weather events, and yet global warming will generate new kinds of weather events that could cause significant harm because of their surprise factor.&nbsp; This paper is primarily about the methodology of estimating harms – it does not provide firm conclusions or numerical estimates of the likely harms, especially in the long run where there is great uncertainty about possible climate changes and harms. It also points out certain issues that need to be addressed, and key questions to be answered, for those who assert that the harms will be high, or that the harms will be low.&nbsp;&nbsp; <br><br>In the literature, there is major disagreement on the size of likely harms from global warming, with scientists and activists warning that global warming is an existential threat requiring an immediate transition to non-carbon emissions technologies, while economists and modelers’ Integrated Assessment Models (IAMs) predicting much smaller harms, about 0-4% of GDP income reduction for a global temperature increase of 2-4°C.&nbsp; I argue that neither side provides a reasonable forward-looking methodology for measuring the likely harms to human society from climate change.&nbsp; In particular we should account for how human resilience and adaptation can significantly reduce the impact of most foreseeable climate events and changes, but we should be aware that surprise and extreme events and major climate changes could cause large harms.&nbsp; <br> <br>I recommend that an alternative methodology be used, that builds a bottom-up approach with a more granular analysis based on likely mechanisms of harm.&nbsp; The analysis should be performed for each type of climate event of concern, such as storms, heat and cold waves, floods, droughts, wildfires, and sea level rise.&nbsp; Rather than relying on a single metric of harm, I recommend using multiple metrics for measuring harms, including deaths, damages, subpopulation harms, disruption, discomfort, and biodiversity, with the emphasis on deaths and the impact on human social welfare.&nbsp; Key factors that affect the likely size of harms include the resilience of human society to various likely climate events; the likelihood of adaptation to observed changes; the ability of climate change to surprise us with new and unexpected events; and the presence of certain human co-factors: poverty and the level of development, the impact of war, and government mismanagement.&nbsp; <br> <br><br> <br><br><br><br> The paper provides some tentative conclusions that global warming will increasingly generate significant harms to our way of life, but is unlikely to cause huge casualties in the short run, especially in the developed world.&nbsp; Our improved ability to adapt and handle most adverse climate events is evidenced by the decline of peacetime famines in the last 200 years.&nbsp; Unless a new catastrophic scenario becomes apparent, this is not an existential threat, but we may end up miserable with a significant loss of life, income and quality of life.&nbsp; However, since we are entering uncharted territory, there is a significant level of uncertainty concerning the likely harms we face in the long run.<br>