Food and Water
In this section, we briefly review several broad policy tools for accelerating clean energy deployment, improving efficiency, and phasing out pollution and emissions.
The world invested nearly two trillion dollars in energy projects in 2018 as follows.
Investment trends point to ongoing advancement of renewable energy in the power sector, but little progress in transportation or industry. The International Energy Agency  projects that world investment in low-carbon energy must nearly double by the late 2020s to meet their Sustainable Development Scenario, which is compatible with two degrees Celsius of global warming.
Economists generally believe that a broad carbon price should be a central component of reducing emissions . Following are some estimated costs of reducing emissions by several other policy tools, which may function as alternatives or supplements to carbon pricing.
Research and development is necessary to bring new energy technologies to commercial production, which in turn are necessary for a complete transition away from fossil fuels. Worldwide, corporations spend on energy R&D as follows.
There is social benefit to research and development; when one company develops a new product, it does not capture all the benefits as the product spreads to other companies. Thus, even in the presence of an economy-wide carbon price, there is justification for governments to invest in R&D . Current public investment is as follows.
The cost of a product tends to fall as more is produced. The effect, identified by Wright  in the context of aircraft, can be quantified and modeled. Cost reduction through production is an essential element of bringing a clean energy technology to commercial maturity. Following are observed learning rates for select technologies. The learning rate is the percent cost reduction that is observed for doubling cumulative production.
International agreements, such as the United Nations Framework Convention on Climate Change, Kyoto Protocol, and Paris Agreement, can help reduce emissions, but only if followed by additional policy tools. Evidence from the Kyoto Protocol is weak but suggests that it has resulted in modest emissions reductions.
These values may be offset by the self-selection problem--that countries may have adopted targets that they would have achieved anyway --or the phenomenon of "exporting emissions", or importing emissions-intensive products from countries without climate change targets .
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