As the December 2015 United Nations climate conference came to a close in Paris, representatives from all 195 of the world’s sovereign states applauded their achievement: a global plan intended to slow the growth of greenhouse gas emissions. The representatives cheered, their presidents declared victory, and the world’s pundits split predictably about what had been done. Some thought the agreement was a step toward saving the planet; others thought it a document too weak to achieve its goals.
The “Paris Agreement under the United Nations Framework Convention on Climate Change” is the product of years of negotiation following a widely panned 2009 conference in Copenhagen. It recognizes “that climate change represents an urgent and potentially irreversible threat to human societies and the planet.” Its objective is to put the world onto a path “consistent with holding the increase in the global average temperature to well below 2°C above pre-industrial levels” beginning in 2020, while also “pursuing efforts” to limit the increase to an even lower maximum limit of 1.5°C.
Creating international agreement on this language is a major achievement. But although it has been seen as a turning point, the Paris Agreement represents the easy part of reining in climate change. The harder challenge lies ahead. For reasons of consensus more than science, a globally averaged temperature increase of 2°C has emerged as an acceptable upper limit among policymakers seeking to curb emissions growth. A flaw of the Paris Agreement, as even its ardent supporters concede, is that it relies upon the voluntary pledges of sovereign states that do not currently add up to anything close to a +2°C temperature limit (let alone a +1.5°C limit) at present. Instead, the current commitments place our planet on a path of continued warming, perhaps to as much as 3.5°C, roughly double the agreement’s stated objectives. Its success also implicitly relies on emerging technologies, like carbon capture and storage (CCS), which takes excess carbon dioxide from the atmosphere and deposits it underground. These technologies have yet to be developed on a large scale.
While the limits on change in temperature I’ve cited and the differences between them may seem small, they actually represent enormous shifts in the earth’s climate. A 2.5°C change is huge, equivalent to the difference between the average daily temperatures of New York City’s hottest and coldest…
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