We must start planning to live with the consequences of climate change

Few things should make you as optimistic — or as pessimistic — as the rise of renewable energy. Optimism comes from a new sense of urgency as the UK, Germany and Spain set record highs for use of wind and solar power, and record lows for coal. Even the US can now generate more power from renewables than from coal, and last month, the “Ocean Wind” project in New Jersey was the largest ever offshore wind farm procured by a US state.

Yet pessimism comes from the fact that all of this may not be enough. In our research at UBS, we estimate that to avoid a dangerous level of global warming, the world would need to commission an asset the size of New Jersey’s Ocean Wind every day for the next 30 years, without missing a day. Or put another way: we need to triple wind and solar construction overnight and sustain that new growth rate for decades, with no room for setbacks.

The hard truth is that we are not on track for that. Nor are we close to an overnight technical solution to the many other challenges of the energy transition that must be solved before we can develop a 100 per cent clean energy system.

Of course, these realities do not stop us from telling ourselves fairy tales. The first one is that energy efficiency will save the day. The facts show just the opposite: over 50 years since the oil price crises of the 1970s, we have seen rising energy efficiency in almost all walks of life, yet in the same time period energy demand and carbon emissions have tripled. As the Victorian economist WS Jevons understood already in 1865, the more efficient you become in your use of a fossil fuel, the more valuable that fossil fuel becomes to you, and the more of it you will consume.

The second fairy tale is a type of deus ex machina, a divine intervention usually staged in the last act of a play. Variously we hear that carbon capture, or nuclear fusion, or geoengineering could play this role. Suggestions include sending mirrors into space to reflect away heat, or ploughing crushed volcanic rock into fields to soak up carbon dioxide. These concepts may one day have potential but few are viable today, and with government debt already at levels similar to the period immediately after the second world war, we see little hope for a programme of public sector investment to speed things up.

So the irony remains: the most realistic pathway to mitigate global warming is to deploy existing renewable technologies at maximum scale, and minimum cost, although the world is most likely now too late and too indebted to get the job done on time.

Read more: FT