-Essay-

SAO PAULO — It's the future here, writing with a warning to brace yourself. How I would love to tell you that in 35 years you'll be able to go back in time, fix your mistakes and change history. Sadly, you won't be able to do that.

The United Nations Climate Change Conference in Paris is in just six months for you. I can tell you now that the summit won't be worth the effort or the cost. Consider this your preview: They'll reach a deal to contain greenhouse gas emissions, which is reasonable considering the political conditions of your time. But as only the future can tell you, that's insufficient to contain global warming in this century below the critical limit of 2 °Celsius.

I'm talking to you from 2050, and we're already close to breaking that barrier. That's despite the fact that carbon emissions have fallen almost to zero, a feat that owes more to UberTesla than to the targets set out in the São Paulo Protocol of 2020.

The self-driving electric cars that entrepreneur Elon Musk launched that same year, after he used the profits from his Powerwall home batteries to acquire Uber, brought traffic jams, public transport and air pollution to an end.

The fossil fuel industry, both car manufacturers and oil companies, went bust. The 2029 crash destroyed the industrial world as you know it, but it created a new, better one. Joseph Schumpeter would have loved to see wind turbines and solar panels spreading all over the world like cars did in the 20th century.

But life in megacities has worsened dramatically. In Brazil, heat waves are turning São Paulo into an inferno three or four times every year, with temperatures above 40° Celsius (104° Fahrenheit). These can last for weeks on end, but they're nothing compared to the tragedy of New Delhi, which is now a ghost town like many others across India after monsoon rains disappeared.

The people of São Paulo, Rio de Janeiro and Belo Horizonte have adapted to the extreme heat. Even in lower middle-class suburbs, the humming sound of air conditioners is constant, and the power shortages that once plagued these urban regions stopped after the government decided to subsidize solar panels and lithium batteries with the ProAir program.

The biggest problem is the lack of water, especially in São Paulo. The Cantareira supply system, the city's biggest, never recovered the levels it enjoyed in the early 21st century. There are hopes that the forest replanting in the Piracicaba, Capivari and Jundiaí river basins, initiated a decade ago, will bring some relief, but that won't be before 2070 at best. And that's only if drought doesn't become permanent, like El Niño.

If you could only imagine what the situation is going to be in 2050, you would do a lot more for your children and grandchildren.