The State of the Climate: COP27 and 1.5C

Another Year of Climate Warming

Progress Since COP26

And so the stage was set for COP27.

A Tumultuous COP27

The 27th Conference of the Parties took place for the first time on the African continent, in Sharm el-Sheik, Egypt, with the over-arching theme of "delivering for people and the planet." Over two weeks in November, over 35,000 participants worked to find consensus on a way forward. In his keynote address at COP27, UN Secretary-General António Gutteres called climate change "the central challenge of our century," stating "the fight for a liveable planet will be won or lost in  this decade."

The COP27 presidency of host country Egypt, defined four goals for the conference:

• Mitigation: limit global warming to well below 2ºC and work to keep the 1.5ºC target alive

• Adaptation: enhancing resilience and assisting the most vulnerable communities

• Finance: address the adaptation needs of developing countries, the Least Developed Countries, and Small Island Developing States

• Collaboration: an inclusive "all hands on deck" approach

So, how did it go?

The Paris Agreement committed rich countries to contribute $100 billion per year to assist poor countries with mitigation and adaptation. In the seven years since, the commitment has never been met. Hence the "Finance" goal of COP27. Finance quickly became the defining element of the conference. Key to the negotiations was the issue of "loss and damage" — the consequences of the worst impacts of climate change, which are too severe for less developed countries to adapt to.

COP27 Results

Heated negotiations finally resulted in an ageement to

COP27 and 1.5ºC

After COP27, Climate Action Tracker updated their climate warming estimates for the rest of the century, based on four scenarios, ranging from real world action based on established government policies to an optimistic "best case" scenario. The results are shown in the figure below. The chart shows that continuing with current government policies and actions around the world will blow right through the Paris Agreement targets. (Note that the predicted temperatures on the CAT thermometer are median values of the range of estimates — the 50/50 probability point. Half of the estimaes are lower than the median and half are higher. Thus the Policies & action scenario estimates range from 2.2ºC to 3.4ºC, with a median of 2.7ºC.) Current "Policies and Actions" will lead to a global average temperature in 2100 well over the 2ºC target, and possibly over 3ºC. What about the 1.5ºC goal? Estimates by the Global Carbon Project place the remaining "carbon budget" for 1.5ºC – that is, the amount of CO2 that can still be emitted for a 50% chance of staying below 1.5ºC of warming – at 380 gigatonnes of CO2 (GtCO2). (A gigatonne is a billion metric tons.) At our current rate of emissions of more than 40 GtCO2 per year, we will exhaust this budget in just nine years. Cutting global CO2 emissions to zero by 2050, in line with limiting warming to 1.5ºC, would require them to fall by about 1.4GtCO2 every year. This is roughly the same as the drop in emissions in 2020 as a result of worldwide COVID-19 lockdowns. Put another way, global emissions will have to fall by almost 50% by 2030 to "keep 1.5 alive." As the graphic below demonstrates, keeping 1.5 alive would require an unrelenting and precipitous decline in CO2 emissions. As the saying goes, "you can't get there from here." The

Within the next five years, it is likely that we will experience our first year with a global average temperature 1.5ºC above pre-industrial levels.

This is certainly worrisome, but it is far from the end of the world. 1.5ºC was always an aspirational target — a stretch goal. Changes to the climate are on a continuum — we don't fall off a cliff when the temperature exceeds 1.5ºC. As climate scientists are fond of saying "every tenth of a degree matters." We're already experiencing climate impacts at 2022's 1.2ºC, and they will be worse at 1.5ºC and still more serious at as temperatures continue to climb. (We'll discuss just how serious later in this article.) But for some people, 1.5ºC is very important, indeed.

Why is 1.5ºC so important?

The origin of the 1.5º and 2ºC targets enshrined in the Paris Agreement owes more to 2015 diplomacy and realpolitik than to hard science. At the time, 2ºC was agreed by the developed countries to be a threshold above which our interference with the climate system might become dangerous. However, "dangerous" is in the eye of the beholder. A group of poor countries and Small Island Developing States held out for 1.5ºC because sea level rise at warmer temperatures would inundate their low-lying communities. In order to achieve a consensus, the parties finally agreed not only to a "well below" 2ºC target, but also to "pursuing efforts to limit the temperature increase to 1.5°C." Seen through the lens of 2022's climate disasters, 1.2ºC of warming is already proving pretty dangerous. Given that, it's tempting to predict that every tenth of a degree warmer might make things just a little bit worse. Unfortunately, it's more complicated (and worse) than that. The problem lies in "tipping points" that exist within elements of the Earth system. In fact, we will see that climate tipping points are critically sensitive to climate warming at 1.2ºC and above.

Tipping Points

The concept of tipping points originated in the ominously named branch of mathematics called Catastrophe Theory. In general terms, a tipping point is defined as a point at which slow, reversible change becomes irreversible, often with dramatic consequences. A tipping point example in a natural system is an avalanche. The snow on a steep slope is stable as the buildup of snow slowly approaches and then reaches the tipping point, and the irreversible snowslide that results is definitely a "dramatic consequence." Climate system tipping points are on a much slower timescale and impact a much larger region. As climate warming pushes the system beyond the tipping point the system can develop a positive feedback loop, rendering the system change "self-perpetuating," and thus irreversible. In 2000, author Malcolm Gladwell popularized the sociological application of the tipping point concept with his best seller "The Tipping Point - How Little Things Can Make a Big Difference." Around the same time, the concept of climate system tipping points was introduced into mainstream climate change policy discussions by the Intergovermental Panel on Climate Change (IPCC). At that time. large scale climate change tipping points were thought to be associated with global climate warming exceeding 5ºC above pre-industrial levels. As a result, tipping points were unfortunately not a major concern in crafting the Paris Agreement. Ongoing research and improved climate models summarized in recent IPCC Reports suggests that tipping points could be exceeded even between 1 and 2ºC of warming. The IPCC judges the risk of these events occurring is high around 2ºC and becomes very high in the range 2.5-4ºC. This means that the 1.5ºC target is back in the spotlight. Every tenth of a degree matters because we are navigating a potential minefield of climate tipping points as climate warming climbs beyond today's 1.2ºC.

Climate tipping points typically have a large, often irreversible impact, and develop at different rates. As we have discussed previously, loss of the

Greenland

and

West Antarctic

ice sheets may take centuries but could add around 10m to global sea level. Collapse of the Atlantic Meridional Overturning Circulation (

AMOC

), which includes the Gulf Stream, would change European climate, raise sea levels in the North Atlantic by up to a meter, and disrupt monsoons around the tropics including in West Africa and India.

As the AMOC example highlights, crossing one tipping point can affect others. In a cascade of tipping points and coupled interactions, retreat of Arctic sea ice and its associated warming is contributing to melting the Greenland ice sheet, and as the meltwater flows into the North Atlantic it contributes to weakening the AMOC. Such coupled, cascading changes

increase the risk

posed by tipping points.

A research team led by David Armstrong McKay recently published an analysis of the elements of the global climate system at risk, their climate tipping points, and the timescales and impacts of crossing the tipping point. The results are summarized in the figure below.

Tipping Elements in the Earth system. Source: Armstrong McKay et al (2022)

The map shows the location of climate tipping elements in the cryosphere (blue), biosphere (green) and the ocean/atmosphere (orange). The global warming levels at which the tipping points will likely be triggered are indicated by colored markers: below 2ºC (in the Paris Agreement range) - light orange circles; between 2 and 4ºC (committed by current policies and actions) - orange diamonds; and 4ºC and above - red triangles.

So, 2ºC? 2.8ºC? 1.5ºC?

The currently estimated tipping point temperature thresholds should be a wake-up call for policy makers. The Paris Agreement target of less than 2ºC is likely to trigger six major tipping points: including widespread Boreal permafrost thawing; Greenland Ice Sheet and West Antarctic Ice Sheet collapse; and Coral Reef Die-Off.

1.5ºC is better, but not safe either, as 1.5ºC risks crossing multiple tipping points. The risk is compounded as crossing those tipping points can generate positive feedbacks that increase the probability of crossing other tipping points.

Looks like the "highway to climate hell" has a lot of potholes...