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火山喷发对科学家及其气候模型构成了根本性挑战。

众所周知,剧烈的火山喷发会导致地表气温突然下降,多次喷发则会在几十年乃至几个世纪的时间尺度上影响气候变率。

当火山喷发将二氧化硫注入平流层时,会形成气溶胶,从而阻挡阳光到达地球表面。

与人类对气候变化的影响不同,后者发生缓慢且可以在各种社会经济情景下被纳入气候模型进行考量。火山喷发具有突发性,这给气候预测带来了挑战。

目前科学家尚无法预测火山喷发的发生时间、地点以及二氧化硫的排放量。

那么,在进行未来气候预测时,如何考虑火山喷发对气候的影响呢?

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在我们最近发表于《通讯-地球与环境》(Communications Earth & Environment)的研究中,我们表明火山喷发对全球气温预测的不确定性产生了重大影响。

我们的研究结果发现,如果将偶发的火山喷发纳入气候预测,突破《巴黎协定》所设定的1.5C升温上限的时间会略有延迟,但与此同时,未来几十年也将出现更多快速升温和降温的时期。

气候预测中的火山强迫

气候科学家将火山喷发对气候的影响——主要是通过释放出二氧化硫气体进入大气——称为“火山强迫”(volcanic forcing)。

当前的气候模型在进行未来预测时采用一个恒定的火山强迫值,该值是根据1850年至今的历史平均强迫值计算得出的。

国际耦合模式比较计划(CMIP)也是如此,这项全球模型工作为政府间气候变化专门委员会(IPCC)发布的重要评估报告提供基础数据。

然而,这种方法存在显著局限。

首先,历史平均强迫值无法表示火山爆发的偶发性。

大规模火山喷发呈零星分布——有时好多事件集中发生在某几个十年内,有时两个事件之间则可能相隔上百年。

此外,与数千年尺度的记录相比,从1850年至今的参考时期中,发生过的大规模喷发事件 ——指排放超过3太克(Tg)二氧化硫的喷发事件——相对较少。

最后,早期国际耦合模式比较计划气候模型中所使用的火山强迫重建数据并未包含排放量少于3太克二氧化硫的中小规模喷发。

这是因为这些喷发在1980年卫星时代开始之前大多未被探测到。然而,这些体量较小但发生频率更高的喷发事件,在长期火山强迫中贡献了30%至50%。

采取新方法

传统上,气候科学家认为气候预测中主要存在三种不确定性来源:内部变率、模型不确定性和情景不确定性。

其中,“内部”变率是指气候系统内部自然产生的波动,如厄尔尼诺现象;模型不确定性是指不同气候模型之间结果的差异;情景不确定性则涉及未来几十年全球可能的发展路径。

我们的研究结果表明,火山喷发应被明确视为气候预测中第四个重要的不确定性来源。

为了探究在考虑火山强迫不确定性的情况下,气候预测会发生怎样的变化,我们的研究采用了一种概率方法,这一方法建立在Bethke等人于2017年提出的研究基础之上。

为此,我们构建了“随机强迫情景”,其本质是1000种延续至本世纪末的火山活动可能时间线预测。

这些情景基于冰芯中记录的过去1.15万年火山活动历史,以及卫星观测和地质证据。每个情景都呈现了不同的喷发强度、地点、时间和频率的组合。

(在数学中,“随机”系统是指结果包含随机性或不确定性的系统,因此不可预测;这与“确定性”系统相对,后者的结果可以通过初始条件和一套规则或方程完全预测。)

随后,我们利用2015至2100年期间的随机火上强迫和历史平均火山强迫模拟气候预测,研究共享社会经济路径(SSPs)中三种不同排放情景下的升温变化:低排放情景(SSP1-1.9)、与现行气候政策相符的中等排放情景(SSP2-4.5)、非常高排放情景(SSP5-8.5)。

在这一步中,我们使用了一种称为FaIR的简化气候模型,也称“模拟器”。

通过模拟1000种不同的火山未来情况,我们发现在21世纪未来时期火山喷发所引起的气候不确定性,可能超过同期气候系统本身的内部变率。

我们还发现,到2030年代,火山喷发可能占全球气温预测总不确定性的三分之一以上。

下图中能看到这些结果。图中展示了不同来源对总不确定性的影响。火山为橙色、内部变率为深蓝色、气候模型响应为黄色,未来人类排放情景为绿色。

Chart: Annual mean contribution of uncertainties

对1.5C临界值的意义

我们的模拟结果表明,在气候预测中纳入可能的火山活动时间线后,短期内突破《巴黎协定》设定的1.5C升温上限的概率略有下降。

根据不同的排放情景,相较于使用恒定火山强迫的预测,模拟发现超过1.5C升温上限的概率下降了4%至10%。

尽管这一结果听起来似乎令人鼓舞,但未来的火山活动并不能在长期缓和由人类引起的全球变暖。

1815年坦博拉火山的喷发事件就是一个强有力的例证。这次喷发使全球气温平均下降了约0.8C,带来了“无夏之年”,导致欧洲、北美和中国大范围的作物歉收和饥荒。

火山喷发带来的降温效应是短暂的,通常只持续几年,其并不会改变由人类排放所导致的长期变暖趋势。

我们的研究发现,即使考虑多种可能的未来火山活动,在除了最低排放路径以外的所有情景中,全球变暖仍将在几十年内超过1.5C。

即便21世纪火山活动频繁,其对全球变暖的抵消作用也仅占很小一部分——这意味着减排对于实现长期气候目标仍然至关重要。

下方图表展示了在三种排放情景下,使用随机火山强迫(实线)与恒定火山强迫(虚线)时超过1.5C的概率(上图),以及两种强迫方式之间的概率差异(下图)。

Charts: Probability of exceeding 1.5C

十年尺度的气温变率

我们的研究提供的另一个重要发现是:一旦将火山强迫的变率纳入考虑,将更有可能出现极端温暖和寒冷的十年期。

在中等排放情景下,我们发现出现负向十年期趋势——即全球表面温度在某个十年内平均下降——的概率增加了10%到18%。

与此同时,出现极端温暖十年期的概率也随之增加,这反映出火山强迫的变率会同时提高变暖和变冷极端事件发生的可能性。

这一结果凸显了火山喷发如何在十年时间尺度上对全球气温趋势带来显著的波动。

迈向更完善的气候预测

了解火山对气候的影响,对于全面评估农业、基础设施和能源系统在未来所面临的风险至关重要。

使用全面的地球系统模型运行数千种火山情景并不切实际,因为这需要极高的计算资源。但与此同时,当前的方法也存在上文提到的显著局限。

不过,在未来的气候模型工作中,仍有折中方案可行。

即将开展的下一阶段气候建模实验——即CMIP7情景模式比较计划——可以采用更具代表性的“平均”火山强迫基线,这一基线纳入了历史记录中常被遗漏的小型喷发事件的影响。这一偏差现已在用于下一代气候模型模拟的历史火山强迫数据集中得到纠正。

此外,建模团队还应额外运行包含高频和低频未来火山活动的情景,以全面捕捉火山不确定性对气候预测的影响范围。

虽然人类导致的温室气体排放仍是气候变化的主导因素,但若能妥善考虑火山活动的不确定性,将有助于我们获得更全面的未来气候图景及其对社会的潜在影响。

The post 嘉宾来稿:探究火山喷发如何影响气候预测 appeared first on Carbon Brief.

嘉宾来稿:探究火山喷发如何影响气候预测

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Revealed: Scientists tell Colombia fossil-fuel transition summit to ‘halt new expansion’

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Countries attending a first-of-its-kind fossil-fuel summit have been asked to consider “action recommendations” such as “halting all new fossil-fuel expansion” and “reject[ing] gas as a bridging fuel”, according to a preliminary scientific report seen by Carbon Brief.

Around 50 nations will gather in Santa Marta, Colombia from 24-29 April to debate ways to “transition away” from fossil fuels, in the face of worsening climate change and sky-high oil prices.

The talks come after a large group of nations campaigned for, but ultimately failed, to get all countries to formally agree to a “roadmap” away from fossil fuels at the COP30 climate summit in Brazil in November.

The nations gathering in Santa Marta for the summit co-hosted by Colombia and the Netherlands, call themselves the “coalition of the willing”.

Ahead of country officials arriving in Santa Marta, a global group of academics will gather in the city this week to present and discuss the latest scientific evidence on fossil-fuel phaseout, which will then inform debate among policymakers.

A preliminary scientific “synthesis report” circulated to governments attending the talks and seen by Carbon Brief offers 12 “action insights” for countries to consider, along with a wide range of “action recommendations”.

These recommendations range from “phase out subsidies on fossil-fuel production and consumption” to “kick-start a forum to develop a legal framework to ban fossil-fuel advertisements”.

‘Rapid’ assessment

The preliminary scientific report seen by Carbon Brief – titled, “Action insights for the Santa Marta process” – is the result of some rapid work by an “ad-hoc” group of around 24 scientists.

It is designed to present governments attending the talks with concrete and actionable recommendations for transitioning away from fossil fuels.

The preliminary version, which includes recommendations such as “halting all new fossil fuel expansion”, has already been circulated to governments, with a view that this could help them to prepare for the talks in advance.

It will be further debated and refined by scientists attending the academic segment of the Santa Marta talks, before a final version is made public towards the end of April, Carbon Brief understands.

The process to produce the report began shortly after the conclusion of the COP30 climate summit in Brazil in November, explains its lead author, Dr Friedrich Bohn, a research scientist and co-founder of the Earth Resilience Institute in Germany. He tells Carbon Brief:

“When [Brazil] announced there would be a Santa Marta conference led by Colombia and the Netherlands, I was sitting listening with a small group of scientists. We thought: ‘This is great news, but it should be supported by scientific expertise.’”

One of the members of Bohn’s group had a pre-existing relationship with the Colombian government, allowing a dialogue to quickly be established, he continues:

“In the beginning, the idea was to just write a peer-reviewed paper. But, because of this close connection to the Colombian government and some feedback from them, the synthesis paper evolved.”

The report came out of a “very rapidly evolved process” that relied on the “goodwill” and “enthusiasm” of the academics involved, adds coordinating author Prof Frank Jotzo, a professor of climate change economics at Australian National University. (Jotzo is a former Carbon Brief contributing editor.) He tells Carbon Brief:

“It’s an attempt to get broad coverage on relevant topics from researchers with good expertise and reputation.”

The group of 24 scientists involved spent around two months compiling the “action insights” for the report, drawing on their expertise and the latest available research, says Jotzo.

Given the rapid nature of the report, it does not aim to be “completist”, has not been externally reviewed and did not follow a stringent process for author selection comparable to that used by Intergovernmental Panel on Climate Change (IPCC) reports, he adds.

The contributors to the report currently skew to the global north and include more men than women, adds Bohn.

‘Direct guidance’

In a departure from IPCC reports, the preliminary Santa Marta synthesis report offers “very direct guidance to action”, says Jotzo.

The report lists 12 “action insights”, each with three “action recommendations”. (The list was cut down from a shortlist of about 40-50 insights, Carbon Brief understands.)

One of the most striking in the draft is “action insight 5”, which says:

“Take immediate measures to prevent future emissions. Ban new fossil infrastructure, mandate deep methane cuts, accelerate electrification and inscribe fossil-fuel phase-down targets in NDCs [nationally determined contributions] and clean-energy pathways support to low and middle income countries (LMICs).”

The accompanying three “action recommendations” include “halting all new fossil-fuel extraction and infrastructure projects ahead of a final investment decision”, “implementing deep, legally binding methane cuts in the energy sector” and “inscrib[ing] targets for fossil-fuel phase down, electrification and green exports in NDCs”.

(The draft report includes multiple references to “phasing out” and “phasing down” fossil fuels, rather than the “transition away from fossil fuels” language that was, ultimately, agreed by countries at the COP28 UN climate talks in Dubai in 2023.)

Another action insight says “public support for climate action is broadly underestimated and undermined by interest groups, but it can be strengthened by debunking greenwashing narratives”.

One recommendation for this insight is that nations “reject natural gas as a bridging technology and CCS [carbon capture and storage] techniques as scalable compensation”.

In a letter introducing the report to governments and civil society, the scientists note that making direct recommendations is a “challenge for our community”, but added:

“However, in the spirit of a constructive collaboration between science and policymaking, we allowed ourselves to identify some potential courses of action that our community would recommend for each particular issue – and we invite you to weigh these against your own circumstances and pick up whatever seems most useful for you and your colleagues.”

The prescriptiveness of the recommendations – something strictly prohibited in IPCC reports – was an explicit request from the Colombian government, Bohn says:

“The idea of actionable recommendations was introduced by the Colombian government.

“There was some discussion within the team about this. It’s a tricky area when you leave science and move to consultation. Therefore, we agreed, in the end, to call them ‘actionable recommendations’ and to make them as precise as possible, from the scientific perspective.”

Jotzo, a veteran of the IPCC process, tells Carbon Brief that it was “very liberating” to work on a report with a “free-form process”:

“The bulk of policy-related research is very readily deployed to recommendations pointing out what countries could do. The IPCC process, for example, just doesn’t allow that. As far as the summary for policymakers in the IPCC is concerned, it will usually be governments that filter out anything that could be interpreted as a specific recommendation.”

He adds that the hope is that some of the action insights might be reflected in the high-level segment of the Santa Marta conference:

“No one is under any illusions that governments will walk away from the Santa Marta conference and will have made a decision to implement recommendations one, seven and nine – or something like that. But it is a chance to insert directly applicable action points into national and plurilateral policy agendas.”

Colombia calling

The preliminary report will be further debated and refined by scientists attending the “pre-academic segment” of the Santa Marta talks.

This is taking place from 24-26 April, ahead of the “high-level segment” involving ministers and other policymakers from 28-29 April.

The pre-academic segment will also separately see the launch of a new advisory panel on fossil-fuel transition and a scientifically led roadmap for how Colombia can transition away from fossil fuels, Carbon Brief understands.

The high-level segment is expected to be attended by representatives from around 50 countries, including COP31 host Turkey and major oil-and-gas producers such as the UK, Canada, Australia, Brazil and Norway.

Countries expected to attend account for one-third of global fossil-fuel demand and one-fifth of global production, according to the Colombian government.

At the end of the conference, countries are due to release a report featuring a “menu of solutions” for transitioning away from fossil fuels, according to Colombia’s environment minister Irene Vélez Torres.

This report is in turn set to inform a global “roadmap” on transitioning away from fossil fuels being developed by the Brazilian COP30 presidency, which is due to be presented at COP31 in Turkey this November.

The Brazilian COP30 presidency offered to bring forward a “voluntary” fossil-fuel transition “roadmap” outside of the official COP process, after countries failed to formally agree to one during negotiations in Belém.

The post Revealed: Scientists tell Colombia fossil-fuel transition summit to ‘halt new expansion’ appeared first on Carbon Brief.

Revealed: Scientists tell Colombia fossil-fuel transition summit to ‘halt new expansion’

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Technical Assessment of Woodside’s Browse Turtle Management Plan

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Technical Assessment of Woodside’s Browse Pygmy Blue Whale Management Plan

To secure their approvals, Woodside had to develop a plan for how they would manage the significant risks to threatened green turtles if the project proceeds. We’ve had two independent scientists provide a technical assessment of Woodside’s management plan for whales and turtles and their findings are gobsmacking.

Woodside’s Browse gas project could make Scott Reef’s unique green turtles extinct.

Woodside’s Browse gas project could delay or prevent the population recovery of the endangered pygmy blue whales that rely on Scott Reef, heightening their extinction risk.

Technical Assessment of Woodside’s Browse Turtle Management Plan

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Low-Producing Oil Wells in Texas Cause Headaches for Landowners

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Jackie Chesnutt, who lives outside San Angelo, is tired of pollution from wells she says should have been plugged years ago. Experts say Texas rules allow companies to defer plugging wells for far too long.

Reporting for this story was supported by a grant from the Fund for Investigative Journalism.

Low-Producing Oil Wells in Texas Cause Headaches for Landowners

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