​Significant increase in global warming

The Kendal power station. Humanity ignored the warning signs about the impact of carbon emissions. (Samantha Reinders, M&G)

The Kendal power station. Humanity ignored the warning signs about the impact of carbon emissions. (Samantha Reinders, M&G)

It’s time for a new climate change concept: fast and slow global warming. A growing understanding of global warming is fundamentally changing projections, showing that the world will warm more, and faster, than previously projected. That means less time for humanity to come to terms with the effect of temperature extremes.

Until now, scientists have had trouble reconciling the two types of warming in their computer simulations. As a result, the world seems to have warmed slower in the last few years than was projected. Writing in the journal Science Advances, a team from Harvard University conclude that this is because the impact of slow global warming has been left out of the simulations. That skews the results and ignored a large chunk of warming.

Fast warming is the record years that we are seeing unfold. That’s 2014, 2015 and then 2016 all taking over as the hottest year in recorded history. Fast is thanks to the greenhouse gas emissions that get trapped in the atmosphere, warming things such as our continents and the layers of air in the atmosphere. Its biggest impact has been on the northern hemisphere, but it has been warming the world as a whole at an increasing rate in the last four decades.

Slow warming is the warming that we know is going into the global climate system but has not yet caused problems. Most of this is happening in the ocean, where a quarter of all the heat the world generate gets absorbed. It is warming that will have a profound impact on the world this century.

Because slow warming mostly goes into the oceans – which are incredibly deep and cold in the case of the Pacific and Southern Ocean – it takes decades and centuries for that warming to translate into perceptibly warmer oceans. That’s why that warming is not currently impacting on the world.

The middle-of-the-road projection used by institutions such as the United Nations Framework Convention on Climate Change says the world will warm by an average of between 1.5°C and 4.5°C this century. Based on this, nearly 200 world governments agreed in Paris two years ago to do what they can to limit that warming to 2°C. Anything over 1.5°C is considered generally catastrophic for the African continent – where the global average is doubled – and for countries that are islands.

The 1.5°C to 3°C gave governments wiggle room; the slower than expected increase in global temperatures meant they had more time to take actions such as cut carbon emissions from industries. But the slower than expected warming continued to confound scientists.

  The Harvard research – Slow climate model reconciles historical and model-based estimates of climate sensitivity – looked at 24 different climate models, and modern as well as ancient temperature records. This allowed it to pick out that current climate models take the warming that is happening now, the fast warming, and project it to stay the same for this century. The models do not include the impact that the slow warming has when it also starts to change global weather patterns.

Key to this is something called climate sensitivity. This is how much the average global temperature rises as a result of an increase of carbon levels in the atmosphere. Two hundreds years ago, when the Industrial Revolution kicked off, levels were at 250 parts of carbon per million parts of air. Now they are at 410 parts per million; the highest level in human history.

The computer models currently look at fast warming and say that, for each doubling of carbon in the atmosphere, global temperatures increase by 3°C. That’s the basis of our current projections for how the world will warm this century. But, when slow warming is included, those models conclude that the world will warm by 4.5°C for every doubling of carbon emissions.

Emissions look likely to be double the pre-Industrial Revolution levels in the next couple of decades.

This means that the world will not just warm by 1.5°C this century, making the goal of lowering carbon emissions a critical one. The Harvard research points to a world that is likely to be 4.5°C hotter this century, and possibly 6°C hotter.

In a 4.5°C scenario, rising sea levels and storms make life in Cape Town, Durban and Port Elizabeth a battered affair. On the Highveld, half of the year will be spent in days where the temperature sits in the high 30s and low 40s.

Humanity ignored the warning signs about the impact of carbon emissions. Now it’s locked into warming where ecosystems collapse, wars unfold over resources and mass migration becomes necessary for survival. This is a scenario where those starting out with the most resources survive. Few of those people are on this continent.

But maybe engineers will find a way to suck all the carbon out of the atmosphere. With little progress on lowering emissions, this is increasingly the scenario that politicians are banking on.

Sipho Kings

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