比尔·盖茨关于气候变化的发言引起轩然大波，他的观点是否正确？

When Bill Gates speaks, people listen. His contributions to tackling global problems have been nothing short of extraordinary, from funding cutting-edge vaccine development to supporting an array of groundbreaking initiatives on climate change. At New York Climate Week in September, his perspectives on climate change did not go unnoticed–and even made waves.

Essentially, his argument is that emissions will peak and then start to go down. They won’t go down as fast as we want them to, so temperatures will continue to rise. Reversing this trend will require massive carbon removal. The goal of staying below 2 degrees Celsius (much less 1.5) appears lost, but we will not find ourselves in worst-case scenarios, and it is unlikely we will go above 3C. Planting trees will not solve the climate problem, he says. Doing climate policy by brute force will not work either. Better to invest in new technologies for carbon removal, clean energy, and electric vehicles and to implement policies like carbon taxes that could fund future green technologies.

It’s a solid argument, but one that depends on nature playing its part in the transition. There is no chance we can limit the worst effects of climate change without saving our remaining ecosystems.

Here are two things to consider. First, there is a large untapped mitigation potential from nature which could offer a substantial contribution towards stabilizing our climate. Second, there is the presence of so-called tipping points which could make unfeasible climate strategies that already require a massive volume of carbon removals.

A straightforward calculus

Let’s start with the contribution of nature to mitigating climate change. There is scientific consensus that to have a decent chance of staying within 2 degrees, the global community needs to cut emissions by 13 to 15 gigatons by 2030. That’s the equivalent of more than three times the emissions of the EU, and this is on top of existing efforts.

Where could these emission reductions come from? The 6th Assessment Report of the Intergovernmental Panel on Climate Change shows that the near-term mitigation potential of halting ecosystem loss, restoring degraded ecosystems, and improving forest management is on par with those of solar, wind, and nuclear. The contribution of nature to close the gap has been estimated at between 4 and 7 Gt/year. Tapping this potential puts us closer to the 2030 goal. It is still a daunting task, but a feasible one.

It is challenging to construct a case in which the non-nature sectors deliver sufficient emission reductions and removals in time to keep us from significantly overshooting the 2030 and 2050 mitigation goals. While there are important mitigation efforts underway in the renewable and transportation sectors, it is becoming increasingly clear that the speed of transition is not enough. Climate policy is also affected by what is politically palatable.

Then, there are the possible tipping points: situations in which a system transitions, perhaps irreversibly, toward a new equilibrium. Tipping points make decarbonization trajectories much more uncertain and can land us in dangerous territory. For example, evidence is mounting that continued deforestation of the Amazon could trigger a change in regional precipitation patterns, and in turn, an irreversible conversion of the rainforest into savannah with a massive release of carbon into the atmosphere. Hit a tipping point like that and the likelihood of a worst-case climate scenario looks increasingly real. The conservation of ecosystems is like buying a fire insurance policy: You may never have to use it, but it is a good idea to have one. Stopping and reversing ecosystem loss as soon as possible should be a priority, not just because of the immense biodiversity and social benefits they provide, but because of their immense carbon storage potential too.

Where it gets complicated

Policies that ban deforestation, for example, can be impactful. But as Mr. Gates rightly says, policies can be reversed. Finding cheaper substitutes for palm oil, soy, and meat, just to mention some drivers of deforestation, would also be important contributions. But as long as the conservation of nature carries little to no economic value, converting forests and other ecosystems will continue to take place.

A necessary condition to keeping ecosystems standing is to make nature more valuable alive than dead. Carbon markets and programs that reward people and communities for tangible results in preserving nature are some ways to accomplish that. Increasing the price of forest carbon and private sector investment in high-quality emission reductions from nature would be a game-changer. Carbon emissions from nature loss are real–bringing them to net zero will provide transformative reductions. Technological advances in measuring forest loss, as well as changes to protocols by which emissions reductions are calculated, validated, and verified, are already producing high-quality carbon credits, which companies can–and should–buy to compensate for unabated carbon emissions.

Recent research that analyzed transactions reported by over 7,000 companies shows that those engaged in the carbon market are nearly twice as likely to be decarbonizing their operations. They are investing three times more in reducing emissions than companies that steer clear of credits. They are also 3.4 times more likely to have science-based climate targets. In other words, most companies that participate in the carbon market are not getting a free pass on internal decarbonization.

Mr. Gates is right–we need to focus on the tools we have available to reduce carbon emissions. However, there is a global consensus that we need the energy, transportation, construction, and other sectors to increase decarbonization efforts, while simultaneously increasing funding and incentives for ecosystem conservation and restoration. We need to invest in nature-based solutions to fill the gap that other sectors won’t.

We need an everything-all-at-once approach. There are many things that must happen to reduce emissions–but we have the tools and solutions. We need to use them all–if we want to stand a chance of reaching our climate goals.

Gabriel Labbate is the head of the climate mitigation unit at the UN Environment Programme’s ecosystem division.