In an interview with Reuters television, the 17-year-old said governments would only be able to mount a meaningful response once they accepted they needed to transform the whole economic system. "We need to see it as, above all, an existential crisis. And as long as it's not being treated as a crisis, we can have as many of these climate change negotiations and talks, conferences as possible. It won't change a thing," Thunberg said, speaking via video from her home in Stockholm. "Above all, we are demanding that we need to treat this crisis as a crisis, because if we don't do that, then we won't be able to do anything," Thunberg said. Thunberg joined several thousand people, including climate scientists, economists, actors and activists in signing an open letter climateemergencyeu.org urging European leaders to start treating climate change like an "emergency." The letter was made public on Thursday, a day before a European Council summit where countries in the 27-member EU will try to reach a deal on the bloc's next budget and a recovery package to respond to the economic shock of the coronavirus pandemic. Demands in the letter included an immediate halt to all investments in fossil fuel exploration and extraction, in parallel with a rapid ending of fossil fuel subsidies. It also called for binding annual "carbon budgets" to limit how much greenhouse gas countries can emit to maximise the chances of capping the rise in average global temperatures at 1.5C, a goal enshrined in the 2015 Paris climate accord. "We understand and know very well that the world is complicated and that what we are asking for may not be easy. The changes necessary to safeguard humanity may seem very unrealistic," the letter said. "But it is much more unrealistic to believe that our society would be able to survive the global heating we're heading for, as well as other disastrous ecological consequences of today's business as usual." The letter called for climate policies to be designed to protect workers and the most vulnerable and reduce economic, racial and gender inequalities, as well as moves to "safeguard and protect" democracy.