Why California’s carbon manure math doesn’t add up

为什么加州的“牛粪碳算术”行不通

Something stinks in California’s climate policies. Years ago, the state set up a system that pays cattle farmers across the country to turn the methane emitted from cattle manure into natural gas, encouraging the dairy sector to produce a gas we burn instead of one that just pollutes the air. It’s become wildly popular because the subsidies are extremely lucrative. 加州的各项气候政策中弥漫着一股“臭味”。多年前，该州建立了一套系统，向全国的养牛户支付费用，将牛粪排放的甲烷转化为天然气，鼓励乳制品行业生产一种可供燃烧的气体，而不是任由其污染空气。由于补贴极其丰厚，该项目变得非常受欢迎。

But a growing body of research suggests the program is a case study in the shortcomings of our preferred approaches to climate action. Instead of simply forcing industries to directly cut their pollution or pay for it as a cost of doing business, legislators have repeatedly opted to set up convoluted incentive systems that swap climate responsibilities between parties and regions. 但越来越多的研究表明，该项目是我们在气候行动中偏好的方法存在缺陷的一个典型案例。立法者没有选择直接强制行业减排或将其作为经营成本支付，而是反复选择建立复杂的激励机制，在不同方和不同地区之间进行气候责任的“置换”。

As studies have shown again and again, these carbon offsetting and trading schemes often dramatically overstate the emissions reductions actually achieved in the one place that matters: the atmosphere. The dairy program illustrates a particular version of this problem, muddling the impacts of different types of greenhouse gases in a way that researchers argue will lock in more warming in the future. 正如多项研究所反复证明的那样，这些碳抵消和交易计划往往极大地夸大了在最关键的地方——大气层——所实现的实际减排量。乳制品项目展示了这一问题的特殊版本，它混淆了不同类型温室气体的影响，研究人员认为这种做法将导致未来出现更多的升温。

Despite this and other concerns, California regulators decided in 2024 to extend parts of the program beyond 2050. And a recent proposal by the state’s air resources board could send millions of additional dollars to dairy farmers as part of a plan that would ease restrictions on major greenhouse-gas producers. 尽管存在这些担忧，加州监管机构仍决定在2024年将该项目的部分内容延长至2050年之后。此外，加州空气资源委员会最近的一项提案可能会向奶农额外提供数百万美元，作为放宽对主要温室气体排放者限制计划的一部分。

Here’s how the system works: The state’s climate regulations require the transportation fuels industry to lower the carbon dioxide levels in its products over time—or purchase credits from other parties that cut fuel emissions, including cattle farmers. Dairies generally spray cattle manure into giant open lagoons, where microbes gobble up organic matter and produce methane as a by-product. 该系统的运作方式如下：加州的气候法规要求运输燃料行业随着时间的推移降低其产品中的二氧化碳水平，或者从其他减排方（包括养牛户）那里购买信用额度。奶牛场通常将牛粪喷入巨大的露天泻湖中，微生物在那里吞噬有机物并产生甲烷作为副产品。

But if farmers set up what are known as anaerobic digesters, the sludge is redirected into covered vessels that capture the biogas, which can be converted into natural gas and injected into a pipeline. It can then be used to fuel certain vehicles or generate electricity in a power plant. Either way, petroleum companies can pay those farmers for Low Carbon Fuel Standard (LCFS) credits, to meet regulatory requirements in lieu of reducing the emissions from their own fuels. 但如果农民安装了所谓的“厌氧消化池”，污泥就会被重新引导至封闭容器中以捕获沼气，这些沼气可以转化为天然气并注入管道。随后，它可用于为特定车辆提供燃料或在发电厂发电。无论哪种方式，石油公司都可以向这些农民支付低碳燃料标准（LCFS）信用额度，以满足监管要求，从而无需减少其自身燃料的排放。

Burning biogas in a bus or turbine still releases carbon dioxide, but the idea is that this process reduces market demand to extract natural gas from the ground and avoids the release of methane, which is a far more powerful greenhouse gas (at least initially). In fact, methane is so much more powerful that under California’s program, “adding one average biogas-powered vehicle to the fleet would produce enough LCFS credits to cover the deficits incurred by 26 similar gasoline-powered vehicles,” according to Aaron Smith, a UC Berkeley economist. 在公交车或涡轮机中燃烧沼气仍会释放二氧化碳，但其理念是，这一过程减少了从地下开采天然气的市场需求，并避免了甲烷的释放，而甲烷（至少在初期）是一种威力大得多的温室气体。事实上，甲烷的威力如此之大，以至于加州大学伯克利分校的经济学家亚伦·史密斯（Aaron Smith）表示，在加州的计划下，“在车队中增加一辆普通的沼气动力汽车，所产生的LCFS信用额度足以抵消26辆同类汽油动力汽车造成的排放赤字。”

But there’s a problem with this carbon math. California assumes that methane exerts about 25 times the warming effect of carbon dioxide over a 100-year period. That’s not how it really works in the atmosphere, though. Methane is very powerful, but it also breaks down quickly, generally within a couple of decades. Meanwhile, carbon dioxide builds up cumulatively in the atmosphere—and much of whatever we emit will continue heating up the planet for hundreds to thousands of years. 但这种碳算术存在一个问题。加州假设甲烷在100年内的升温效应约为二氧化碳的25倍。然而，在大气层中，实际情况并非如此。甲烷的威力确实很大，但它分解得也很快，通常在几十年内就会分解。与此同时，二氧化碳在大气中累积，我们排放的大部分二氧化碳将在数百年甚至数千年内持续加热地球。

So, in effect, the state has created a system that reduces short-term warming at the cost of increasing all-but-permanent warming. Any methane that digesters capture today would have caused extra-powerful warming if released, but by 2050 that effect would have mostly faded away. Meanwhile, that additional carbon dioxide we permitted in its place could continue warming the world for millennia. 因此，实际上，该州建立了一个以增加几乎永久性的升温为代价来减少短期升温的系统。消化池今天捕获的任何甲烷如果被释放，本会造成极强的升温，但到2050年，这种影响大部分会消失。与此同时，我们取而代之排放的额外二氧化碳可能会在未来几千年里持续加热地球。

It is a good idea to cut methane emissions, and dairy digesters achieve this (though not always as effectively as hoped). But we can’t swap a decrease in short-lived greenhouse gases for an increase in long-lived ones if we hope to keep global temperatures within relatively safe levels in the coming century, as researchers have long warned. We have to slash both. 减少甲烷排放是一个好主意，奶牛场消化池也确实实现了这一点（尽管并不总是像预期的那样有效）。但正如研究人员长期警告的那样，如果我们希望在下个世纪将全球气温保持在相对安全的水平，我们就不能用减少短寿命温室气体来换取长寿命温室气体的增加。我们必须同时削减两者。

The problem I keep returning to, after years of covering carbon markets and offsets, is this: We need to clean up every sector, completely, over the next few decades. It’s increasingly untenable for so many of our climate ambitions to turn on getting one industry to make progress on paper by paying another one to reduce emissions, at a point when every business in every industry needs to be racing toward net zero. 在报道了多年的碳市场和抵消机制后，我不断思考的问题是：在接下来的几十年里，我们需要彻底清理每一个行业。在每一个行业的每一家企业都需要竞相实现净零排放的时刻，我们太多的气候雄心竟然依赖于让一个行业通过向另一个行业支付减排费用来在纸面上取得进展，这已变得越来越站不住脚。

It’s time to move past the idea that we need to reward sectors for doing us the favor of not polluting the atmosphere, and simply require them to stop unloading the huge environmental burden of their business onto society. 是时候摒弃那种“我们需要奖励那些不污染大气的行业”的想法了，我们应该直接要求它们停止将巨大的商业环境负担转嫁给社会。