# Problem

## Causal logic

Greenhouse gases (GHGs) emitted by human industrial activity will increase the Earth’s surface temperature. This will worsen the productivity of ecosystems, reduce agriculture and fishing output, exacerbate water shortages, exacerbate weather-related risks, worsen human health, and displace people.1 These factors could also contribute to conflict in troubled regions.

## Evidence

The evidence base for anthropogenic climate change is robust. IPCC regards it as “extremely likely” (95-100% chance) though not “virtually certain” (99-100% chance) that anthropogenic greenhouse gas emissions are the dominant cause of observed warming.2

Warming of 2°C or more is commonly expected. There are small chances of warming to 4°C or greater. Assuming the most pessimistic out of four climate scenarios (RCP8.5), it is ‘likely’ (66-100% chance) that climate change will be between 2.6 and 4.8°C by 2100,3 which would imply a small but notable chance of warming exceeding 4.8°C (“perhaps around 10%”4). Climate scientist Zeke Hausfather claims that we seem closest to RCP8.5 but it’s too hard to really tell.5

Wagner and Weitzman create a more precise forecast with a clearer pessimistic conclusion, that there is a 11% overall chance of climate change exceeding 6°C if concentrations reach 700ppm.6

Varying amounts of evidence substantiate specific consequences expected of climate change. The strength of the link between climate change and severe weather is disputed. The strength of the link between climate change and conflict is disputed.7

## Scope

Giving What We Can investigated the short run direct human impacts of climate change and estimated that it takes 258,200 tonnes of emissions to cause one death by 2054.8

There have been numerous efforts to quantify the long run economic costs of climate change, generally looking at 2100 as the benchmark year. A 2018 statistical test of climate models found that the best performing models estimate a 1-2% loss from unmitigated warming.9 One metanalysis from 2017 estimated a 1.6% loss to global GDP from 3°C of warming,10 but another estimated a 9-10% loss.11 A survey of economists in 2015 revealed that the mean of their median estimates of the costs of past-and-future climate change of 3°C was 10.2% of world GDP by 2090.12

GiveWell argued that the risk of extreme climate change adds substantially to the expected cost.13 Quadratic damage functions (favored by Nordhaus and Moffat14 for instance) suggest that 6°C of warming would cause four times as much damage as 3°C.

A disproportionate amount of the damage from climate change is expected to fall upon poorer, developing nations. Therefore the human welfare costs will be greater than those suggested by the global GDP estimates.

Climate change will disrupt the environment, but it’s not clear whether this would increase or decrease wildlife suffering.15

John Halstead found that there is no support for the claim that climate change is a direct existential risk.16 Climate change may still indirectly contribute to existential risks by worsening and disrupting civilization, although a similar thing may be said for many other problems such as disease and governance.

## Views

80,000 Hours regards extreme risks from climate change as “sometimes recommended”, appropriate for some people though not their highest rating.17

The 2017 EA survey did not ask directly about climate change, but it did ask about environmentalism as a cause area. Environmentalism had the fourth highest number of people calling it the top priority, out of nine cause areas in the survey. It also had the fourth highest number of people saying that no EA resources should go towards it.18

# Solutions

## Clean energy

Research and lobbying can accelerate the adoption of clean energy.

In 2019, Let’s Fund found that public spending on clean energy R&D is the most effective climate intervention. They recommend donations to the Information Technology and Innovation Foundation.19

In 2013, Giving What We Can estimated that Cool Earth is the most efficient climate change charity out of those considered, reducing CO2e at approximately $0.81/tonne.22 However, a more recent report explains that the initial report was overly optimistic.23 ### Other impacts Forest protection has some other benefits for sustainability and public health. Forest protection also increases the wildlife population, which may be good or bad depending on the quality of wild animal experiences. There is disagreement on whether there is more suffering than happiness among wildlife.24 25 ## Carbon pricing Economists mostly agree that the government should implement market solutions (a carbon tax or cap-and-trade) rather than regulations.26 27 Carbon taxes are in turn better than cap-and-trade.28 They are a better way of raising government revenue than broad hikes to income taxes.29 However, Let’s Fund argues that carbon pricing can still lead to under-investment in clean energy R&D, because it can let companies rely on technologies that will not be as useful for curbing future emissions in the developing world. In addition, carbon pricing is a less neglected and tractable policy goal. Therefore carbon price lobbying is a lower philanthropic priority than clean energy R&D.30 Eliminating fossil fuel subsidies follows the same path as establishing carbon pricing. However, Let’s Fund finds that it’s too minor and intractable to be a high priority.31 ### Other impacts Carbon pricing will have benefits for public health. It will reduce US reliance on foreign energy. It will preserve the store of fossil fuels in case they are needed in the future. ## Geoengineering Geoengineering could shape the Earth’s climate and counteract the greenhouse effect. Halstead argues that solar geoengineering research should not be pursued right now.32 ## Vegetarianism Promoting vegetarian/vegan diets would reduce greenhouse gas emissions. However, even assuming a very low figure ($11) for the average cost to convert someone to vegetarian, it costs approximately \$7/tonne of CO2e avoided, making it a poor choice for fighting climate change.33

Personally switching from an average diet to a vegan diet only saves 1 tonne of CO2e per year.34

### Other impacts

Vegetarian and vegan diets reduce farm animal suffering.35 They also generally have public health and sustainability benefits due to reductions in pollution and antibiotics. There is limited evidence that they increase nutritional health.