Could Climate Change Trigger a Financial Crisis?气候变化能引发金融危机吗？

付迎杰

In recent years regulators have begun warning about the threat that climate change poses to the stability of the financial system. Following its strategy review in July， the European Central Bank （ECB） will assemble a “climate change action plan”. Mark Carney， the former governor of the Bank of England， warned of financial risks from climate change as long ago as 2015. In America the Commodity Futures Trading Commission last year published a 200-page report beginning “Climate change poses a major risk to the stability of the US financial system.” But progressive Democratic politicians are calling on President Joe Biden not to reappoint Jerome Powell as the chairman of the Federal Reserve， partly because they think he has done too little to eliminate climate risk.

Just how damaging does climate risk stand to be， though？ Early stress tests by central banks and disclosures of companies are starting to shed light on the question. For the most part， the evidence that it could bring down the financial system is underwhelming. But a lot hangs on whether governments set out a clear path for reducing emissions， such as through carbon taxes and energy-efficiency standards， giving banks enough time to prepare.

Climate change can affect the financial system in three ways. The first is through what regulators describe as “transition risks”. These are most likely to arise if governments pursue tougher climate policies. If they do， the economy restructures： capital moves away from dirty sectors and towards cleaner ones. Companies in polluting industries may default on loans or bonds; their share prices may collapse.

The second channel is financial firms’ exposure to the hazards of rising temperatures. Attributing individual natural disasters to climate change is tricky， but the Financial Stability Board， a group of regulators， estimates that global economic losses resulting from weather-related catastrophes went from $214bn in the 1980s， in 2019 prices， to $1.62trn in the 2010s. These losses are often borne by insurers （though over time the costs should be passed on to customers through higher premiums）.

The financial system could also be exposed to any wider economic damage caused by climate change， say if it triggered swings in asset prices. This third channel is harder to quantify. Academic estimates of the effect of 3°C of warming （relative to pre-industrial temperatures） veer from financial losses of around 2% to 25% of world GDP， according to the Network for Greening the Financial System， a group of supervisors. Even the gloomiest estimate might prove too rosy if climate change triggers conflicts or mass migrations.

Perhaps the worst-case scenario for the financial system is where transition risks crystallize very suddenly and cause wider economic damage. In 2015 Mr. Carney described a possible “Minsky moment”， named after Hyman Minsky， an economist， in which investors’ expectations about future climate pol-icies adjust sharply， causing fire sales of assets and a wide-spread repricing of risk. That could spill over into higher borrowing costs.

The value of financial assets exposed to transition risk is potentially very large. According to Carbon Tracker， a climate think-tank， around $18trn of global equities， $8trn of bonds and perhaps $30trn of unlisted debt are linked to high-emitting sectors of the economy. That compares with the $1trn market for collateralized debt obligations （CDOs） in 2007， which were at the heart of the global financial crisis. The impact of losses， however， would depend on who owns the assets. Regulators might be especially concerned about the exposures of large， “systemically important” banks and insurers， for instance.

Preliminary stress tests conducted by central banks suggest that the impact of climate change on these sorts of institutions might be manageable. In April the Banque de France （BDF） released the results from such an exercise. It found that French banks’ exposures to transition risks were low. Claims on insurers， though， did rise as a result of worse droughts and flooding， by more than five times in some regions.

In a recent paper the ECB and the European Systemic Risk Board found similar results. The exposures of euro-area banks and insurers to the highest-emitting sectors were “limited”， although losses in a “hot-house world” scenario where temperatures rise by 3.5°C compared with pre-industrial times were more severe. Still， in both cases， banks’ losses on their corporate loan books were only around half the level of those in the regular stress tests1 of euro-area lenders， which they were deemed to be well-capitalized enough to pass.

Those findings are consistent with an exercise by the Dutch central bank （DNB） in 2018， which found that the impact on Dutch financial firms from transition risks was “manageable”. In its most severe scenario， there was a sudden change in climate policy alongside rapid progress in renewable energy development， causing a “double shock” for companies and a severe recession. Even then， banks’ capital ratios fell by about four percentage points. That is sizeable， but still less than what the banks experienced in this year’s regular stress tests by the European Banking Authority， which they were deemed to pass.

To what extent are these stress tests realistic？ Mark Campanale of Carbon Tracker is skeptical， pointing out that most firms are using out-of-date models. If auditors were ever to stress companies’ assets against a much lower oil price， the associated write-downs could trigger a collapse in investor sentiment of the sort regulators fear， he claims. Nor do the stress tests include a full-blown Minsky crisis.

Yet in other respects they are conservative. Most of the tests used an accelerated time frame—five years in the DNB and BDF cases—in effect assuming that firms are stuck with the balance-sheets they have today. But it seems reasonable to think that banks and insurers will change their business models as the climate transition progresses， curbing the impact on the financial system. The BDF ran a second exercise where firms were allowed to make realistic changes to their business models over 30 years. Unsurprisingly， that allowed banks to sharply reduce lending to fossil-fuel sectors， and insurers to raise premiums.

Nonetheless， the stress tests reveal the importance of giving firms time to adapt. And that makes a predictable path for government policy important. The BDF found that credit losses were highest when policy was delayed and there was a sudden transition. Perhaps the most plausible scenario in which climate change affects financial stability is one in which governments dawdle， and then have no choice but to take drastic action in the future.

最近几年，监管机构已经开始警告人们气候变化将威胁到金融系统的稳定。在2020年7月份的战略审查之后，欧洲中央银行将制订一项 “气候变化行动计划”。英国央行前行长马克·卡尼早在2015年就警告过气候变化会带来金融风险。在美国，商品期货交易委员会去年发表了一份长达200页的报告，开头写道：“气候变化对美国金融系统的稳定性构成重大风险”。但民主党进步派政治家呼吁总统乔·拜登不要重新任命杰罗姆·鲍威尔为美联储主席，部分原因是他们认为鲍威尔在消除气候风险方面做得太少。

不过，气候风险的破坏性到底有多大？各国中央银行的早期压力测试和各公司披露的消息让这个问题初露端倪。在大多数情况下，气候风险可能导致金融系统崩溃的证据是不充分的。但这在很大程度上取决于政府是否制定了明确的减排路径（比如通过征收碳税和推行能效标准），给银行足够的准备时间。

气候变化可以通过三个方面影响金融系统。第一个方面是通过监管机构所描述的“转型风险”。如果政府推行更严厉的气候政策，这些风险最有可能出现。如果他们这样做，经济就会重组：资本从重污染行业转移到更清洁的行业。高污染行业的公司可能会拖欠贷款或出现债券违约;他们的股票价格也可能会暴跌。

第二个方面是金融公司对气候变暖存在风险敞口。将个别自然灾害归咎于气候变化有欺骗性，但金融稳定委员会（由各国金融管理机构组成）估计，与天气有关的灾难造成的全球经济损失从20世纪80年代的2140亿美元（按2019年价格水平计算）上升到2010年代的1.62万亿美元。这些损失通常由保险公司承担（尽管最终这些成本将通过更高的保险费转嫁给客户）。

如果气候变化引发了资产价格的波动，金融系统也可能遭受气候变化造成的更广泛的经济损失。第三种风险更难量化。央行与监管机构绿色金融网络（由各国金融监管机构组成）称，学术界对气候变暖3摄氏度（相对于工业化前的温度）的影响做出估计，相关金融损失占全球GDP的比例将从 2%左右增至25%。如果气候变化引发冲突或大规模移民，后果将不堪设想。

对金融系统来说，也许最糟糕的情况是转型风险突然具体化，并造成更大范围的经济损失。2015年，卡尼先生描述了一個可能会出现的“明斯基时刻”（以经济学家海曼·明斯基的名字命名），即投资者对未来气候政策的预期急剧调整，导致资产的低价抛售和广泛的风险重新定价。这可能会导致更高的借贷成本。

面临转型风险的金融资产可能价值巨大。根据气候智库“碳追踪”的数据，全球约有18万亿美元的股票、8万亿美元的债券和约30万亿美元的未上市债务与经济中的高排放行业有关。与之相比，2007年的担保债务凭证市场规模为1万亿美元，是全球金融危机的核心所在。然而，损失的影响将取决于谁拥有这些资产。例如，监管机构可能会特别关注“具有系统重要性”的大型银行和保险公司的风险敞口。

各国中央银行进行的初步压力测试表明，气候变化对这些机构的影响可能是可控的。2020年4月，法国央行发布了这样的测试结果。它发现法国银行转型风险敞口很小。但是，由于干旱和洪涝灾害加剧，对保险公司的索赔确实增加了，在一些地区增加了五倍以上。

在最近的一份文件中，欧洲央行和欧洲系统性风险委员会也得出了类似的结果。欧元区银行和保险公司对碳排放量最高的行业的风险敞口“有限”，尽管在“温室世界”（温度比工业化前上升3.5摄氏度）的情形下损失更为严重。不过，在这两种情况下，银行在企业贷款账面上的损失只有欧元区银行定期压力测试中的一半左右，它们被认为资本充足，足以通过压力测试。

这些发现与荷兰央行2018年的一项测试一致，该测试发现转型风险对荷兰金融企业的影响是“可控的”。在形势最严峻的情景中，随着可再生能源开发取得快速进展，气候政策也发生了突然变化，对企业造成了“双重冲击”和严重的经济衰退。即使如此，银行的资本充足率也下降了大约四个百分点。这一降幅十分显著，但仍然低于今年欧洲银行管理局对银行进行的定期压力测试中的降幅（银行已经通过测试）。

这些压力测试在多大程度上有现实意义？智库“碳追踪”的馬克·坎帕纳莱对此持怀疑态度，他指出，大多数公司都在使用过时的模型。他说，如果审计机构在对公司资产进行压力测试时设置了低得多的石油价格参数，相关的资产减值可能会引发投资者情绪崩溃这种令监管机构担忧的情况。这些压力测试也不包括全面爆发的明斯基危机。

然而，在其他方面，压力测试是保守的。大多数测试使用了一个加速的时间框架——在荷兰央行和法国央行是5年——实际上是假设公司无法摆脱它们今天的资产负债困境。但似乎有理由认为，随着气候转型的进展，银行和保险公司将改变它们的商业模式，用以遏制对金融系统的影响。法国央行进行了第二次测试，允许企业在30年内对其商业模式进行务实的改变。不出所料，这使得银行大幅减少对化石燃料部门的贷款，使保险公司提高保费。

尽管如此，压力测试揭示了给公司预留足够时间去适应的重要性。而这使得政府政策的可预测路径变得重要。法国央行发现，当政策被推迟并突然转型时，信贷损失最高。也许气候变化影响金融稳定最有可能出现的情况是，政府拖拖拉拉，然后别无选择，只能在未来采取激进的措施来应对。