Analysis: The future sketched out in a new United Nations report – saying the world will now inevitably cross the 1.5C warming threshold – is objectively catastrophic. Exactly how catastrophic it gets is up to us.

That is pretty clearly cold comfort for future generations facing several metres of sea-level rise, Pacific Islanders whose homes are increasingly likely to vanish under the waves or the billions of people subjected to extreme heat, intense storms and every climatic horror in between.

At the same time, it is the most important decision everyone alive on this planet today will make. Yesterday, perhaps, that decision was whether or not global warming would exceed 1.5C above pre-industrial levels. We made the wrong choice – although the United Nations notes that decision may have been made in truth some five or 10 years ago.

Today, the decision is how far above 1.5C we will allow the world to warm, how long we will let temperatures peak and whether or how quickly we will bring them back down in the decades and centuries to come.

The difference between the most ambitious climate pathway, which returns warming to below 1.5C by the end of the century, and a business-as-usual approach where temperatures hit 2.6C by 2100 with no sign of slowing, is enormous. It is far greater than the difference between 1.5C and 1.6C or 1.8C.

Keeping warming below 1.5C is not possible. But beyond that, the future is still wide open.

Although these are pathways and possible futures which will play out beyond our lifetimes, the United Nations is clear: The future generations who will be most affected are not the ones calling the shots. We are.

“Decisions taken now will influence how high warming rises, how long exceedance lasts, which losses can still be avoided and the capacities available to future generations beyond the peak. Overshoot is not a reason to lower ambition. It is a reason to act earlier, learn faster and sustain cooperation for longer,” the landmark report finds.

So, what are you going to do about it?

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Tipping points

To answer that question, we must first understand how we got here and what our future options are.

While the goal of global climate policy has for some time been to limit warming to no greater than 2C, a growing body of evidence in the early 2010s began to suggest that was well beyond a safe limit for human civilisation.

At the Paris climate talks in 2015, Pacific Island nations managed to secure a more ambitious goal in the accord that resulted: “Holding the increase in the global average temperature to well below 2C above preindustrial levels and pursuing efforts to limit the temperature increase to 1.5C above preindustrial levels, recognising that this would significantly reduce the risks and impacts of climate change”.

In 2018, a special report from the Intergovernmental Panel on Climate Change revealed just how significant the dangers of exceeding 1.5C were. It became a global rallying cry – even as global emissions continued to increase, putting the target further and further out of reach.

The United Nations Environment Programme report released this week confirms what the maths was increasingly suggesting. 1.5C is no longer achievable, in the traditional sense of keeping warming from passing that threshold.

“Temporary exceedance of 1.5C is inevitable under current emissions trajectories and policy settings,” the United Nations finds.

Global temperatures have already exceeded 1.5C in recent years, but the global temperature goal is about the average over decades. There was some slim hope that sufficient action on climate could halt warming just below that threshold. No longer.

“Taken together, the available evidence suggests that the central estimate of human-induced global warming will be crossing 1.5C above pre-industrial levels in the next few years.”

Crossing 1.5C comes with disastrous consequences. To pull just a few from the new report: Even 1.2C implies “future Global Mean Sea Levels some metres higher than present”, “there is a low possibility of corals surviving this century” and “projections indicate declines of up to 14 per cent in global food production by 2050 in the absence of effective adaptation”.

These are just the straightforward consequences of a warming world. But climate change does not play out linearly. There are some parts of the global climate system which will degrade less like a melting ice cube and more like a light switch – on for a long time, then suddenly flicked off.

The exact risk of these tipping points being triggered is not clear, but it’s high enough that we need to take it seriously, the United Nations advises.

“While thresholds and response times remain uncertain, evidence increasingly indicates that sustained warming above 1.5C raises the risk of triggering one or more tipping elements.”

These are things like the Amazon Rainforest, which if it shrinks enough due to deforestation and wildfires could stop producing enough rain to maintain its own ecosystem, and then collapse into a savannah, releasing billions of tonnes of carbon dioxide and destroying precious ecosystems in the process.

Then there’s the “albedo effect”, a technical term for the amount of sunlight reflected by ice sheets and sea ice. As the ice melts, revealing rock and dark ocean, the world absorbs more heat, triggering more ice melt, and then a vicious spiral of self-reinforcing warming and sea-level rise.

Overshoot

As bad as that all sounds – and it is really very bad – we still have agency in this situation. To start with, while we cannot halt warming at 1.5C, it is still up to us whether we stop it at 1.8C or 2C or 2.6C or higher.

The science is clear: The higher temperatures go, the greater the danger. And the non-linear nature of climate change means that a 3C world is not twice as bad as a 1.5C world. It is instead exponentially worse. Or, to put it another way, we still have the power to secure an exponentially better future.

Nor is the global warming peak necessarily where we have to stay. Much of the new report concerns itself with the concept of overshoot pathways, scenarios where temperatures rise above 1.5C and then fall back below that threshold over decades or centuries.

Temporary overshoot has long been a feature of global climate models, in part because emissions trajectories under insufficient climate policy have made it clear that keeping warming to 1.5C or even 2C was virtually impossible without it.

To achieve overshoot, the United Nations says, temperatures must first stop rising, which can only happen if the world hits net-zero carbon dioxide emissions and flatlines emissions of non-CO2 gases like methane.

Then, we must begin removing more carbon dioxide from the atmosphere than we’re adding, while also slashing non-CO2 emissions. That’s the “decline” stage.

Finally, the world would eventually stabilise at a new level of warming, presumably below 1.5C but almost certainly not returning to preindustrial temperatures.

Why not? Because that middle stage, the decline, will be very, very difficult. Although climate models have long relied on large-scale carbon dioxide removal, there are good reasons to think that removal can only scale up so high.

Even in a report calling for returning temperatures to below 1.5C, the United Nations highlights the problems.

At current levels of carbon sequestration – around two billion tonnes a year globally, through tree-planting and restoring wetlands and other carbon-sucking ecosystems – it would take 100 years to take 0.1C off the thermometer.

While we can plant more trees, there are limits to that. Social licence, human rights, the health of ecosystems and competition from agriculture are all barriers to tree-planting as a climate silver bullet. Plus, eventually you run out of land.

As a result, many scientists have turned to carbon capture and storage as a supplement to conventional forms of sequestration. This involves capturing carbon dioxide either at the point of production (a power plant smokestack) or out of thin air and then storing it in underground reservoirs. Often, these are reservoirs which were located and made empty because they had previously stored fossil fuels.

The difficulty with carbon capture and storage is that, according to the Institute for Energy Economics and Financial Analysis, “no one single carbon capture and storage project has ever reached its target CO2 capture rate”.

Even if it did work, there are limits to how much storage we have. “Just maintaining net-zero CO2 emissions could exhaust current estimated storage capacity in sedimentary basins by 2200,” the United Nations finds. “Overall, even optimistic carbon dioxide removal scaling is unlikely to deliver a temperature reversal beyond a few tenths of a degree this century.”

Later, the report says: “Even under scenarios where net-negative CO2 emissions reach 10 GtCO2 per year, or around a quarter of present-day CO2 emissions, warming may only reverse by about 0.05C per decade. In other words, a decade of global warming at the current rate of about 0.25C per decade may take about 50 years to reverse, even under optimistic carbon dioxide removal assumptions.”

Indeed, despite the focus on temporary overshoot, the report notes that while it is technically possible that does not mean it is actually possible.

“Reversing global warming after exceeding 1.5C is theoretically possible. However, it would require sustained net-negative carbon dioxide emissions at globally relevant scales over decades to centuries, supported by deep reductions in methane,” it says.

“Achieving the former would require avoiding CO2 emissions as much as possible while scaling CO2 removal methods. Achieving the latter would require substantial advances in reducing ‘hard-to-abate’ methane emissions, particularly from agriculture. The feasibility of achieving both at the required scale remains uncertain.”

And even if it is all feasible and we manage to actually do it, we don’t know what kind of world we’re going to get. What we do know is the planet we return to some 70-200 years after overshooting 1.5C will not be the one we left.

“Even if a return to below 1.5C is secured, many nations and communities will face irreversible losses and permanently changed conditions,” the report finds.

“Impacts such as continued sea-level rise, species extinctions and ecosystem regime shifts may continue far beyond peak temperatures. Many communities may have relocated or changed livelihoods. Societies will face the challenge of readjustment: agricultural systems reconfigured for higher temperatures may need to be readapted; infrastructure designed for climate extremes may become mismatched; communities weakened by decades of crisis will face a second transition capacity; and maladaptation from mitigation may be an issue.”

Which takes us back to step one: The greatest influence we have right now on how bad things get is how high temperatures peak, since we can’t be sure we’ll get to bring them down. And the thing that decides how high temperatures peak is how long it takes us to stop burning fossil fuels.

What are you going to do?

The situation we have put ourselves in is confronting. It is not just understandable to feel hopeless, terrified, furious or some combination of the three, but rational to feel that way when presented with the frankly irrational and twisted world we are facing.

And yet there are still choices available to us. In my seven years of writing and thinking about climate change, I have found that the natural despair and horror are best kept at bay when I have agency. The psychological literature, too, increasingly shows that taking agency does not just salve our consciences on climate, it makes us more effective as well.

The question I posed at the start of this article was: What are you going to do about it?

I could have asked what we’re going to do about it. But the word “we” has a way of diffusing responsibility. “We” means someone else will take charge. “We” means “you” don’t really have to worry about it. Because that would be the easy thing to do – to put it out of your mind.

Besides, what can you do? You’re just one person. You live in New Zealand, a country of five million at the bottom of the world that produces just 0.2 percent of global climate pollution. Surely this is a problem for “us” (the Government, or China, or Donald Trump) and not “you”.

These are familiar lines. We hear our own political leaders deploy them regularly.

They also sap agency. They sap our ability, as humans, to play a role in determining what happens to our civilisation and what the world our children and grandchildren inherit looks like.

That is the reason why politicians adopt them so readily. But it is not an argument we make about anything else. New Zealanders made up around 0.2 percent of Allied forces in each of the World Wars, but we do not say their efforts and sacrifice were in vain.

So let’s try again: What can you do? You can take the jump – seven lifestyle shifts proven to cut emissions. Climate Club dispatches a weekly newsletter with high-impact actions that take five, 15 or 30 minutes. Go beyond just buying green and activate your climate superpower. You can trap pests, plant trees, vote, take your children out into nature. You can do anything, writes Emily Atkin. Yes, if you must, you can even recycle.

It is a truism to say that every little bit helps. But it is a truism backed by science.

Every tonne of CO2 adds equally to global warming, whether it originates in Guangdong or Los Angeles or Matamata. Every tonne avoided, research has found, keeps nine tonnes of ice locked up in glaciers, 12 cubic metres of sea-level rise at bay, six kilos of rice and a kilo of meat protected from heat stress – whether it would have come from China, America or New Zealand.

Your agency is visible in the array of possible futures we can see before us. It is in the shades of a degree between 1.5C and 2C of warming.

The United Nations report says exactly that: “This report does not assume that future outcomes are predetermined. Rather, it emphasises that a ‘decline’ is not a given. Every fraction of a degree matters: the magnitude of peak warming, the duration of how long we stay above 1.5C and the scale of resulting impacts remain strongly influenced by present actions.

“Every fraction of a degree avoided reduces risks. Every year by which overshoot duration is shortened reduces exposure. Every investment in resilience preserves future options.”

Crossing the 1.5C threshold does not strip any one of us of our agency. Instead, it gives us even more power – and more obligation – to avert the worst outcomes. It will take all of us. But “us” includes “you”.