Weather and climate: in the eye of the storm

By Julio Slingo,  published in the Financial Times, 13 April 2017 (h/t to Larry Kummer)

Julia Slingo is the former chief scientist of the Met Office.

In 1972, fresh from a physics degree at Bristol University, I joined the UK’s national weather service, the Met Office. I liked meteorology because I could look out of the window and see physics in action. Clouds forming in a blue sky, and the wind blowing so often from the west

— it was not immediately obvious why that should be, and I was intrigued. (I learnt later that the UK lies right in the path of the jet stream, a band of westerly winds that circles the mid-latitudes. The jet stream arises from the rotation of the Earth — the Coriolis Force — and because the planet is heated at the equator and cooled at the poles.)

I joined a team building the first climate models, simulating the evolution of the Earth’s atmosphere on the basis of fundamental physical principles. Elsewhere, and based on very similar science, numerical weather forecasting was taking off. I made some of the early calculations of how sensitive the climate might be to increasing levels of carbon dioxide. Little did I know then that this would become one of the defining problems of the 21st century.

In the decades since, simulations produced by these models have become the bedrock of our understanding of how the weather and climate work. With the help of new technologies, such as satellites and supercomputers, these models have revolutionised our thinking: we use them for forecasting from hours to years ahead, and they are central to assessing future climate change and its impacts.

But more than that, for scientists like myself, these models are our laboratories. With them we can find out why our climate varies, and why it now seems to be changing.

It has only been through simulating what the world would have been like without greenhouse gas emissions that we can say with confidence that humans have been the dominant cause of the observed warming since the mid-20th century.

Yet even as our capabilities improve, the challenge for meteorologists is increasing. Our planet’s population is rising, cities are growing rapidly, often along coastlines, and our world is increasingly and intricately interdependent — relying on global telecommunications, transport systems and the resilient provision of food, energy and water. All of these are vulnerable to adverse weather and climate. The additional pressure of climate change poses new questions about how secure we will be in the future.

***

In early 2009, some 37 years after first joining the Met Office, I returned as its chief scientist, attracted by a desire to see my science working for society. It was clear to me that the weather and climate would have considerable direct and indirect impacts on us, perhaps more so than ever before — on our livelihoods, property, well-being and prosperity. It was equally clear that the benefits of access to the best weather and climate science and predictions would be profound.

The Earth’s atmosphere is massively complex and, as a result, the weather we experience varies hugely from place to place and over different times of the year. We cannot understand and forecast our weather in the UK without seeing it in the context of the global atmosphere and, increasingly, the global oceans.

Our forecasts now embrace timescales from a few hours to a decade ahead, and our climate change projections give us scenarios, out to the end of the century and beyond, of how the weather and climate may change in fundamental ways as the Earth responds to rising levels of greenhouse gases.

Increasingly, we look to these simulations to understand the likelihood of hazardous or extreme weather such as storms, heatwaves or prolonged drought — and what these represent in terms of risks to society. In the UK, as in many other parts of the world, we are well aware that nearly all the highest-impact weather events are localised. Flooding regularly costs the country millions of pounds, and can take a huge toll on the lives of those worst affected — yet the areas involved are often only a few kilometres wide.

During my time as chief scientist we were able to implement a new forecasting system based on a model that works at the scale of our local weather. We had been striving for this for many years

— we knew it was feasible scientifically, but the computational power was just not available. With the latest advances in supercomputing and investment by the government, this has become a reality. Now, for the first time, the cloud systems that deliver our rainfall are captured by the model with the level of fidelity needed to predict severe, localised events.

This has proved to be a landmark in weather research and forecasting. It has meant that we could provide the detailed severe weather warnings that were so essential in recent winters for protecting lives and livelihoods against the winds, waves and floods that battered the country. In the St Jude’s Day storm of 2013, for example, and again for Storm Desmond in 2015-16, we were able to alert emergency services, transport providers and local authorities, often more than 24 hours in advance. This meant that temporary flood defences could be deployed, bridges closed, train services rescheduled and plans put in place for rapid post-event recovery.

Beyond the weather, we are also exposed and vulnerable to the Earth’s natural variations in the climate, such as El Niño, the intermittent warming of the tropical East Pacific Ocean that has profound effects around the world, including droughts and wildfires in Indonesia, poor monsoon rains in India and floods in California.

We need to be better prepared for such events, so that we can manage the risks they pose more effectively. The good news is that it’s now possible to predict an El Niño event at least six months in advance. Nearer to home, for the UK and Europe, we have developed the capability to assess the likelihood of a particular kind of winter several months beforehand, so that we can predict, say, a mild, wet winter or a drier, cooler winter — something considered unlikely a few years ago.

Advances in modelling the ‘Earth system’ are bringing about a new age in our science, enabling us to probe in greater detail than ever before the processes and phenomena that shape the world

This has only come about because we have rigorously explored processes in the atmosphere and oceans that determine our seasonal climate, and pushed the resolution of our models to provide much greater realism at the regional scale, again enabled by more powerful supercomputers. As a result there have been major advances in what we call seasonal forecasting, and the potential for further advances is huge.

Within the next few years we should be able to provide early warnings of extended cold spells and heatwaves that will enable health services, energy suppliers and transport providers to be better prepared. We are still learning how best to communicate and utilise the wealth of information in our seasonal forecasts, but recent scientific breakthroughs give us confidence that their potential value is high.

***

And then there is climate change. Temperatures have risen by about 1.0C since pre-industrial times; Arctic sea ice extent has declined by 3 per cent every decade since records began in 1979

— and at a faster rate in summer; sea levels have been rising by about 3mm a year since the early 1990s; each of the past three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. We are more confident than ever that humans have been the dominant cause of the rise in temperatures since the 1950s.

While no extreme weather or climate event can be attributed solely to climate change, after the terrible damage of the 2013-14 winter storms and again the flooding in 2015-16, people inevitably and rightly ask: is this climate change?

There is as yet no “definitive answer” to this question, partly due to the highly variable nature of the UK’s climate (ie our “British weather”), but the evidence we do have, such as increasingly heavy daily rainfall and rising sea levels, suggests that the risks of serious flooding and coastal inundation are growing with climate change. Our job now is to say in greater detail what this might mean for the UK’s weather patterns, so that we can make wise choices about investing in infrastructure to increase our resilience.

We do know that some level of climate change is inevitable regardless of what happens to carbon emissions in the future, because of the accumulation of carbon within the atmosphere. This

means that some level of adaptation will be necessary. How we adapt is a key question. The scale of potential spending on, say, flood defence systems, the risks associated with failure, and the long lifetimes and lead-times involved mean that such investments are likely to be highly sensitive to how climate change evolves over the next two to three decades. We need to be sure that we climate-proof our cities and our infrastructure.

There is no doubt that new and more robust climate projections will be required on a country-by- country level if we are to adapt to the challenges and even exploit the opportunities presented by climate change.

In 2018, the Met Office will deliver its latest assessments of what the UK’s weather might be like in the coming decades, using the same local-scale model that we have recently deployed in weather forecasting. The outputs of this model should help us understand far more about the volatility of our weather in the future, and how extreme weather at the local scale, such as flash floods and storm surges, may affect us.

Looking beyond the next few decades, we also need to assess the longer-term risks of irreversible or dangerous climate change, such as the loss of the Greenland ice sheet, huge releases of methane — a potent greenhouse gas — from melting permafrost, long-term sea level rise and acidification of the oceans. Remarkable progress has been made in building a new generation of models that represent many more components of the Earth, such as ice sheets, vegetation and marine life — now known as “Earth system” models. We need to understand the future evolution of the whole Earth system and how it has evolved in the past under major climatic changes.

This landmark system meant we could provide the warnings that were so essential recently to protect lives against the winds and floods that battered the country

This knowledge will be critical for deciding the pace and depth of climate change mitigation actions. We are learning, for example, that melting permafrost has the potential to release large amounts of carbon into the atmosphere, effectively reducing what we can emit in the coming decades — our allowable carbon budget — if we are to stay within the limit of a global surface temperature increase of 2C, or even 1.5C, as agreed in Paris in December 2015.

Advances in modelling the Earth system are bringing about a new age in our science, enabling us to probe in greater detail than ever before the processes and phenomena that shape the world.

These new capabilities have begun to unlock the benefits of weather and climate intelligence, but much more can be achieved. The science is never “done”; there is always more to learn, and the complexity of our world means that there will always be things we don’t know.

Increasingly, our actions and our responses to environmental change, such as landscape management and flood defences, will influence the environment itself. For this reason, we need to make significant advances in the end-to-end evaluation of environmental risks and benefits. This will require the integration of the physical simulation of weather and climate with areas

such as advanced modelling of the built environment; quantification of the value of natural capital and ecosystem services; understanding of human dynamics; modelling of ecological systems; and new approaches to modelling financial and socioeconomic impact.

***

Last December, I retired after nearly eight years as Met Office chief scientist. It was a pleasure and privilege to lead one of the best environmental research organisations in the world at a time when, more than ever, we depend on skilful, comprehensive predictions of the weather, climate and the broader environment.

It is worth reflecting on the words of vice-admiral Robert FitzRoy, the captain of the Beagle who took Charles Darwin on his momentous voyages but who was also the founder of the Met Office. After the wreck of the Royal Charter in a terrible storm in 1859, he wrote to The Times:

“Man cannot still the raging of the wind, but he can predict it. He cannot appease the storm, but he can escape its violence, and if all the appliances available for the salvation of life [from shipwreck] were but properly employed the effects of these awful visitations might be wonderfully mitigated.”

More than 150 years ago, FitzRoy embarked on the long journey of making predictions as a means of reducing and managing the impacts of severe weather and climate change, and his words speak across the years to us today.

From the global to the local and from hours to decades, our understanding of weather and climate and the predictions we make will enable us to plan for the future and keep us safe.

Guest post by David Middleton

Introduction

When debating the merits of the CAGW (catastrophic anthropogenic global warming) hypothesis, I often encounter this sort of straw man fallacy:

All that stuff is a distraction. Disprove the science of the greenhouse effect. Win a nobel prize get a million bucks. Forget the models and look at the facts. Global temperatures are year after year reaching record temperatures. Or do you want to deny that.

Source

This is akin to arguing that one would have to disprove convection in order to falsify plate tectonics or genetics in order to falsify evolution.  Plate tectonics and evolution are extremely robust scientific theories which rely on a combination of empirical and correlative evidence.  Neither theory can be directly tested through controlled experimentation.  However, both theories have been tested through decades of observations.  Subsequent observations have largely conformed to these theories.

Note: I will not engage in debates about the validity of the scientific theories of plate tectonics or evolution.

The power of such scientific theories is demonstrated through their predictive skill: Theories are predictive of subsequent observations.  This is why a robust scientific theory is even more powerful than facts (AKA observations).

CAGW is a similar type of theory hypothesis.  It relies on empirical (the “good”) and correlative evidence (the “bad”).

The Good

Carbon dioxide is a so-called “greenhouse” gas.  It retards radiative cooling.  All other factors held equal, increasing the atmospheric concentration of CO2 will lead to a somewhat higher atmospheric temperature.  However, all other things are never held equal in Earth and Atmospheric Science… The atmosphere is not air in a jar; references to Arrhenius have no signficance.

Atmospheric CO2 has risen since the 19th century.

Humans are responsible for at least half of this rise in atmospheric CO2.

While anthropogenic sources are a tiny fraction of the total sources, we are removing carbon from geologic sequestration and returning it to the active carbon cycle.

The average temperature of Earth’s surface and troposphere has generally risen over the past 150 years.

Atmospheric CO2 has risen and warming has occurred.

The Bad

The modern warming began long before the recent rise in atmospheric CO2 and prior to the 19th century temperature and CO2 were decoupled:

The recent rise in temperature is no more anomalous than the Medieval Warm Period or the Little Ice Age:

Over the past 2,000 years, the average temperature of the Northern Hemisphere has exceeded natural variability (defined as two standard deviations from the pre-1865 mean) three times: 1) the peak of the Medieval Warm Period 2) the nadir of the Little Ice Age and 3) since 1998.  Human activities clearly were not the cause of the first two deviations.  70% of the warming since the early 1600’s clearly falls within the range of natural variability.

While it is possible that the current warm period is about 0.2 °C warmer than the peak of the Medieval Warm Period, this could be due to the differing resolutions of the proxy reconstruction and instrumental data:

The amplitude of the reconstructed temperature variability on centennial time-scales exceeds 0.6°C. This reconstruction is the first to show a distinct Roman Warm Period c. AD 1-300, reaching up to the 1961-1990 mean temperature level, followed by the Dark Age Cold Period c. AD 300-800. The Medieval Warm Period is seen c. AD 800–1300 and the Little Ice Age is clearly visible c. AD 1300-1900, followed by a rapid temperature increase in the twentieth century. The highest average temperatures in the reconstruction are encountered in the mid to late tenth century and the lowest in the late seventeenth century. Decadal mean temperatures seem to have reached or exceeded the 1961-1990 mean temperature level during substantial parts of the Roman Warm Period and the Medieval Warm Period. The temperature of the last two decades, however, is possibly higher than during any previous time in the past two millennia, although this is only seen in the instrumental temperature data and not in the multi-proxy reconstruction itself.

[…]

The proxy reconstruction itself does not show such an unprecedented warming but we must consider that only a few records used in the reconstruction extend into the 1990s. Nevertheless, a very cautious interpretation of the level of warmth since AD 1990 compared to that of the peak warming during the Roman Warm Period and the Medieval Warm Period is strongly suggested.

[…]

The amplitude of the temperature variability on multi-decadal to centennial time-scales reconstructed here should presumably be considered to be the minimum of the true variability on those time-scales.

[…]

Ljungqvist, 2010

The climate of the Holocene has been characterized by a roughly millennial cycle of warming and cooling (for those who don’t like the word “cycle,” pretend that I typed “quasi-periodic fluctuation):

These cycles (quasi-periodic fluctuations) even have names:

These cycles have been long recognized by Quaternary geologists:

Fourier analysis of the GISP2 ice core clearly demonstrates that the millennial scale climate cycle is the dominant signal in the Holocene (Davis & Bohling, 2001).