The Trump administration has signalled its intentions of backing out of commitments the USA made at the Paris meeting of the UN Climate Convention in 2015. This matters because the USA accounts for about 14% of global greenhouse gas emissions. Their reneging on their pledge may also encourage others to join them in free loading on other people's efforts.

Any dilution of mitigation commitments relative to the Paris Agreement is potentially disastrous.The Agreement has the central goal of keeping the increase in global average temperature to well below 2 degrees Celsius (°C) above pre-industrial levels.  The median cost optimal path for ensuring 66% probability of staying within the  2°C goal requires emission in 2030 to be 42 gigatonnes of CO₂ equivalent (GtCO₂e) and turn negative after 2075 so that we stay within the allowable cumulative limit of 1000 GtCO₂e of which around 80% will be used up by 2030. The 1.5°C aspiration included in the agreement will remain that and it is very likely that we will cross this limit within a decade.

The commitments made under the Paris Agreement fall short of this cost optimal path by 12-14  GtCO₂e in 2030. Moreover very few countries are currently on track to meet their commitments. UNEP's Emissions Gap report says that of the G20 countries, who account for the bulk of the emission burden, only EU, India and China are on track, while the others will need further policy action to meet their pledges.

What makes this much more disturbing is some recent scientific work that suggests that the 2°C goal itself is too high to prevent major risks. James Hansen, a highly respected climate scientist, and his associates have produced an assessment whose frightening forecast  is that "modeling, paleoclimate evidence, and on-going observations together imply that 2°C global warming above the preindustrial level could be dangerous." Basically they forecast that global warming would trap a hot water belt below a colder ocean surface and that this would lead to faster ice melt, a much more rapid rise in sea levels and an impact on ocean circulation patterns that would have huge terrestrial impacts.

There are tangible warning signs that global warming may be happening faster than expected

• The change in average concentrations  of  CO₂  from February 2015  to February 2016  was 3.76 parts per million at the Mauna Loa Observatory in Hawaii, the highest recorded per year increase. The  CO₂  concentration has crossed 400ppm and is unlikely to fall below it. If this rate of increase continues, the 450ppm limit, consistent with the 2°C goal, will be reached by 2030.
• A reported pause in global warming between 1998 and 2014 was false, according to US-British research published recently.
• Human-induced climate change was directly linked to individual extreme events in half the studies of such events published by the Bulletin of the American Meteorological Society between 2011 and 2014,
• Over the past three decades the area of sea ice in the Arctic has fallen by more than half and its volume has plummeted by three-quarters.  The Arctic will be free of sea ice in the summer by 2040 rather than  2070 as earlier predicted.
• The India Meteorological Department (IMD) says the India is on an average 0.6° C hotter than a century ago. Until 2015, 13 of Indiaʼs 15 warmest years ever were after 2000 and 2016 was the warmest year since 1901. The incidence, intensity and length of heat waves is increasing.

The challenge therefore before the world community is twofold-how to deal with the rogue administration in Washington, and how to accelerate action beyond the Paris Agreement commitments.

On the first question, let USA walk out of the Paris Agreement, as they did out of the Kyoto Protocol. Trump reckons that, like any bazaar bargainer, if he walks away, he will be chased and offered concessions. Do not chase him.  Negotiating any revision with the USA will weaken the Paris commitments when the evidence requires us to strengthen them.   

Yet the USA is not a write-off for climate action and will contribute despite the Trump administration.  States like California that are well ahead on climate action and coalitions that have taken on voluntary actions promise to  deliver significant mitigation benefits that will counter  part of  Trump's roll back of Obama's energy initiatives.  The strong US technology based venture system is supporting renewables, electric vehicles and energy efficiency,  Many major corporations have advertised their support for the U.S. staying in the Paris Agreement and the US environmental movement has launched a vigorous lobbying campaign. Even within the administration there are supporters of the Paris Agreement led by Ivanka Trump and reputed to include the Secretaries for State and Defence.

EU leaders and Xi Jinping have warned Washington not to renege on the Paris commitment. India has been inexplicably silent and must speak up. These leaders must openly endorse the climate positive initiatives outside the administration in the USA and encourage their corporate groups, research establishments and environmental activists to connect with their counterparts in the USA.

Accelerating action beyond the Paris commitments may be both more difficult and more easy - more difficult because of the resistance from those who will be stuck with stranded fossil fuel assets and more easy because alternatives are rapidly becoming competitive and attracting capital and high grade technological talent. The EU, China and India can readily improve on their Paris commitments  and should take the lead by announcing enhanced mitigation goals to respond to the new warning signals and more specific initiatives like deadlines for phasing out of fossil fuel based transportation or goals for passive space heating and cooling.

The end of the fossil fuel industry and the emergence of a new renewables based energy economy, with attendant changes in transportation, urban design and buildings is the Schumpeterian creative destruction of the next few decades. We should move with this tide of history and leave President Trump to command the waves to roll back.