Overturning 1.5°C: Give science a chance

Credit: Alejandro Ospina

In 2005, Professor Mary Christina Wood together with a fierce litigator named Julia Olson began constructing a legal architecture for securing children’s rights to a life-sustaining climate system. Understanding that the principle “for every rights violation, there must be a remedy” forms the core of democratic legal systems everywhere, the lawyers reached out to one of the world’s most highly respected climate scientists, Dr. James Hansen, to pinpoint a systemic climate remedy.

2008: Climate science and climate cases converge

In 2008, Hansen co-published the seminal paper, Target Atmospheric CO2: Where Should Humanity Aim?, finding that the average level of atmospheric CO2 must remain below 350 parts per million (ppm) to rebalance Earth’s energy, preserve a planet to which life is adapted, and protect fundamental rights. This ceiling is known as the 350 ppm limit. Since the world has already overshot this limit—atmospheric CO2 was 385 ppm in 2008 and averages 419 ppm today—courts needed to know the scientific pathway to reduce emissions and restore 350 ppm. Understanding this, Wood and Olson asked Hansen to build on his 2008 findings and identify a viable emissions reduction pathway to return atmospheric CO2 to a level that would be safe for humanity.

In a second seminal paper, Hansen and 17 leading scientists restate the necessity of reducing atmospheric CO2 to 350 ppm and map out a concrete, achievable emissions reduction pathway to stabilize the climate system. For the scientific community, the findings became a cornerstone upon which to continue to build solutions for our planetary emergency. For some litigators, the findings were adopted as the scientific standard to protect fundamental rights in courts.


2011: Igniting the “rights turn”

Readied with a viable remedy, the legal team at Our Children’s Trust—alongside lawyers, scientists, and young people—made history, filing a wave of coordinated legal actions in all 50 US states, the US federal government, and several countries to secure climate rights. These were the first climate rights cases on behalf of young people ever filed.

In a nationally-televised interview, Wood explained, “Every [legal action] filed in every state and against the federal government asks for the same relief. And that is for the government . . . to bring down carbon emissions in compliance with what scientists say is necessary to avert catastrophic climate change.”

When these actions hit the headlines, legal experts reacted in various ways, calling the rights approach “legally brilliant,” “legally reckless,” or “legally impossible.” Ultimately, this pioneering wave of youth-initiated actions set in motion the “rights turn” in strategic climate litigation.


2015–2016: Solidifying the “rights turn”

By 2015, a trio of groundbreaking court decisions established that the rights approach was poised to prevail. First, the decision in Urgenda v. Netherlands established that climate inaction is a violation of internationally recognized human rights. Subsequently, in Leghari v. Pakistan, the court described climate change as a defining challenge of our time, confirmed that Pakistan’s lack of action on climate change had infringed on the right to life, dignity, and property, and held that the right to a clean and healthy environment must be guided by principles of generational equity. Next, the US District Court of Oregon issued a game-changing decision in Juliana v. United States, writing, “[T]he right to a climate system capable of sustaining human life is fundamental to a free and ordered society.” This ruling marked the first time a court had declared a constitutionally protected, climate-specific right.


Today: Securing the “science turn”

Inspired by the 2011 wave of cases and promising signals from the courts, youth have brought dozens of climate suits to tribunals around the globe, establishing that long odds are worth the wager. Having attained the “rights turn,” the next step is to defy the odds again and secure the “science turn.”

In every rights-based climate case, the judge asks, “What standard must the court use to assess whether government promotion of fossil fuels—or failure to act on climate change—has breached fundamental rights?” In other words, “What is the safe zone?”

In 2015, as the “rights turn” took hold, another landmark event occurred: nearly 200 countries signed the Paris Agreement, saying “yes” to the goal of limiting the global temperature rise to 1.5°C–2.0°C, despite resounding warnings from scientists that allowing global average temperatures to rise to—and remain at—1.5°C is “highly dangerous.” The finding that 1.5°C is dangerous is an agreed-upon scientific fact corroborated by volumes of scientific evidence and the United Nations’ own scientific body, the Intergovernmental Panel on Climate Change (IPCC).

In 2018, the IPCC’s 600+ page report cataloged the imminent harm humanity will endure as the temperature hits 1.5°C. It concludes, “1.5°C is not considered ‘safe’ for most nations, communities, ecosystems and sectors and poses significant risks to natural and human systems.” The IPCC repeated this warning in 2022 and again in 2023. Every day, scientists publish more evidence of the dangers of allowing temperatures to rise and remain at 1.5°C. Yet, a comprehensive study of rights-based climate litigation finds that, instead of using the best available science, which calls for humanity to limit atmospheric CO2 to 350 ppm, litigators continue to argue that governments need only aim for the politically negotiated Paris target of 1.5°C.

Since judicial decisions are only as good as the evidence they are based upon, it is critical that lawyers present the most up-to-date and best available evidence to tribunals in lieu of outdated targets set by politicians. To do otherwise locks bad science into law. For instance, in 2016, over 2,000 older women brought a case against Switzerland, asserting that climate-induced heatwaves violated their right to life and family life, asking the court to order Switzerland to meet the 1.5°C target. In 2016, the Earth’s average surface temperature was ~1.07°C above pre-industrial levels. Yet, this case asks the court to sanction a target that is ~43% higher than the temperature at the time the violations at issue occurred.

In June 2023, the Commission of Small Island States (COSIS) submitted a 100+ page brief to the International Tribunal for the Law of the Sea. The brief underscores that “up-to-date scientific data is a critical yardstick against which States’ environmental due diligence obligations must be measured” and catalogs the numerous human rights harms that would befall small island nations at 1.5°C. Nevertheless, COSIS concludes that a 1.5°C target would be an acceptable legal standard.

Former US Supreme Court Justice Stephen Breyer shares that judges are “generalists” and must rely on lawyers to present evidence to help courts understand how to interpret and apply the law. This is particularly true in climate cases since many judges do not have a background in climate science, and even where they do, the field is dynamic, with new relevant findings being published constantly. 

Consequently, two underlying misperceptions must be overcome: the fear that asking courts to recognize the 350 ppm limit is “legally impossible” and the misperception that 1.5°C is the “best we can do.” There are moments in history when doing our best is not good enough. We must instead do what is necessary. The climate emergency presents one of those moments. In the recent past, many thought rights-based climate litigation would never succeed. For those who believe courts will not base their decisions on what science says is necessary, I say, give courts a chance.