When Beto O’Rourke launched his presidential campaign, I was impressed. On multiple occasions, including as recently as April, O’Rourke backed calls to effectively zero out all domestic emissions of the greenhouse gases that cause climate change by 2030, and said we’re screwed if we aim for anything less.

On Monday, he shifted the goalposts back. He released a detailed climate plan, his first policy proposal of his campaign. There’s a lot to like. He pledged to make climate action a day one priority and included an expansion of resources for climate resiliency and adaptation. But he also pushed back the timeline to achieve net-zero emissions to 2050. Our movement was sad to see him let up on his ambition as he rolled out the specifics, before we even give it a try.

Just in the last year and a half, floods in the midwest, Hurricane Maria in Puerto Rico and fires in California have devastated American communities. Waiting 20 more years is not an option for people like Mikala Butson, a 22-year-old Californian who I met recently while on the Road to the Green New Deal tour, whose mother and brother fled from flames in the Camp fire last November. Her hometown, Magalia, was nearly erased from the map alongside Paradise. Ninety-three people died. Tens of thousands lost their homes.

Some took issue with my criticism of the timeline of O’Rourke’s plan for being too sharp or unforgiving. They pointed out that this is the most ambitious climate platform yet proposed by a presidential candidate. They are right. But this is the terrible paradox of climate policy in 2019 – even a historically ambitious plan can fall far short of what’s needed. Our measuring stick is not politics; it is physics, and the urgent demands of justice for all on the frontlines of climate disaster.

Last year, the UN Intergovernmental Panel on Climate Change (IPCC) said that we have just 12 years to radically transform our economy to avoid catastrophic climate change of more than 1.5C (2.7F). Globally, they said, we need to achieve net-zero emissions by 2050. In order to reach that goal globally, the US must do much more, much faster. The US can’t aim to get to net-zero emissions by 2050, as O’Rourke’s new plan proposes.

It is absurd to suggest that developing nations such as India, South Africa, Indonesia and Brazil, which are growing rapidly and improving the quality of life for their people, should reach net-zero emissions at the same time as the US. Rich, advanced economic powerhouses like the US have the responsibility to move much more quickly in order to help move the rest of the world toward net-zero emissions by 2050 – otherwise millions of lives will be lost.

The Green New Deal calls for a 10-year mobilization to achieve net-zero greenhouse gas emissions. This week, many pundits and wonks have criticized us, saying that goal is not possible. They have told us we’re young and naive, that we should keep our goals tied to what’s possible right now.

We don’t know if this goal of achieving net-zero emissions in a decade is possible, and many experts tell us it’s not. Maybe O’Rourke talked to those same experts who told him to push back his ambition over these past few weeks. But it is by putting out an ambitious goal and doing everything in our power to achieve it that we will push what’s possible.

If you want to argue it’s not worth setting an ambitious goal and fighting like hell to get there, you need to be prepared to explain that decision to the people already suffering from the current levels of warming. To the 800,000 people in India where my family is from who were displaced by record floods last year. To the children whose parents burned alive in their cars trying to escape flames last year in California. To the kids in sub-Saharan Africa who are growing up malnourished because there hasn’t been enough rain to grow food.

I believe it is our duty as a generation to push against the limits of the possible and protect as many lives as we can from disasters that can be prevented. Young people are looking for a president who will fight hard for what our generation and our world deserves – and have the courage to rally our nation to put everything we’ve got behind doing it. Even if we fail trying, we will get much further much faster, and prevent much more damage, in the process. After all, mitigating the climate crisis is not an all-or-nothing endeavor. If setting goals that push the boundaries avoid even a tenth of a degree of warming, that additional effort will be the difference between life and death for millions.

When Franklin D Roosevelt said we would build a historic air force of 185,000 planes to defeat the Nazis, we barely had an airlines industry. We were producing only about 3,000 planes a year. We didn’t know if we could do it, but we knew we had to try. By the end of the second world war, we had produced more than 324,000 military aircraft (in less than five years). It was the same situation when John F Kennedy said we would send a man to the moon in 10 years; we didn’t know if it was possible, but we knew it was worth trying.

When America believes it can do the impossible, we make the impossible inevitable. That’s what the Green New Deal is all about – daring America to dream again, and calling on every sector of society to come together to do what needs to be done.