The Industrial Revolution Kick-Started Global Warming Much Earlier Than we Realised

Giant clam on Great Barrier Reef (Wikipedia)

by Helen McGregor, University of Wollongong; Joelle Gergis, University of Melbourne; Nerilie Abram, Australian National University, and Steven Phipps, University of Tasmania, The Conversation: https://theconversation.com/the-industrial-revolution-kick-started-global-warming-much-earlier-than-we-realised-64301

In the early days of the Industrial Revolution, no-one would have thought that their burning of fossil fuels would have an almost immediate effect on the climate.

But our new study, published today in Nature, reveals that warming in some regions actually began as early as the 1830s. That is much earlier than previously thought, so our discovery redefines our understanding of when human activity began to influence our climate.

Determining when global warming began, and how quickly the planet has warmed since then, is essential for understanding how much we have altered the climate in different parts of the world. Our study helps to answer the question of whether our climate is already operating outside thresholds that are considered safe for human society and functional ecosystems.

Our findings show that warming did not develop at the same time across the planet. The tropical oceans and the Arctic were the first regions to begin warming, in the 1830s. Europe, North America and Asia followed roughly two decades later.

Surprisingly, the results show that the southern hemisphere began warming much later, with Australasia and South America starting to warm from the early 20th century. This continental-scale time lag is still evident today: while some parts of Antarctica have begun to warm, a clear warming signal over the entire continent is still not detectable.

The warming in most regions reversed what would otherwise have been a cooling trend related to high volcanic activity during the preceding centuries.

Global warming got underway much earlier in the north.

By pinpointing the date when human-induced climate change started, we can then begin to work out when the warming trend broke through the boundaries of the climate’s natural fluctuations, because it takes some decades for the global warming signal to “emerge” above the natural climate variability.

According to our evidence, in all regions except for Antarctica, we are now well and truly operating in a greenhouse-influenced world. We know this because the only climate models that can reproduce the results seen in our records of past climate are those models that factor in the effect of the carbon dioxide released into the atmosphere by humans.

These remarkable findings were pieced together from the most unusual of sources - not thermometers or satellites, but rather from natural climate archives. These include coral skeletons, ice cores, tree rings, cave deposits and ocean and lake sediment layers, all of which record the climate as they grow or accumulate. These archives provide long records that extend back 500 years - well before the Industrial Revolution - and provide a critical baseline for the planet’s past climate, one that is impossible to obtain otherwise.

Corals can help reveal the climate of centuries past, long before weather records began. Eric Matson/AIMS, Author provided

But why is there no clear warming fingerprint yet seen across Antarctica? The answer most likely lies in the vast Southern Ocean, which isolates the frozen continent from the warming happening elsewhere. The westerly winds that circulate through the Southern Ocean around Antarctica keep warm air masses from lower latitudes at bay. Ozone depletion and rising greenhouse gas concentrations during the 20th century have also caused this wind barrier to get stronger.

The Southern Ocean currents that flow around Antarctica also tend to move warmer surface waters away from the continent, to be replaced with cold deeper water that hasn’t yet been affected by surface greenhouse warming. This process could potentially delay Antarctica’s warming by centuries.

Ocean insulation

The delay in warming observed in the rest of the southern hemisphere is something we do not yet fully understand. It could simply be because fewer records are available from the southern hemisphere, meaning that we still don’t have a full picture of what is happening.

Alternatively, like Antarctica, the southern hemisphere’s oceans could be holding back warming - partly through winds and currents, but perhaps also because of “thermal inertia”, whereby the ocean can absorb far more heat energy than the atmosphere or the land before its temperature markedly increases. Bear in mind that the southern half of the globe has much more ocean than the north.

Essentially, then, the coolness of the southern hemisphere’s vast oceans could be “insulating” Australasia and South America from the impact of global warming. The question is, for how long?

If our evidence of delayed warming in the southern hemisphere holds true, it could mean we are in in for more climate surprises as global warming begins to overcome the thermal inertia of our surrounding oceans. Could the recent record warming of Australian waters, and the subsequent damage to the Great Barrier Reef, be an early sign that this is already occurring?

Recent research suggest that the mass bleaching event of the reef was made 175 times more likely by climate change. Following the recent severity of such extremes, a better understanding of how anthropogenic greenhouse warming is already impacting the southern hemisphere is critical.

What to do about it

Leading scientists from around the world met in Geneva last week to discuss the goal of limiting average global warming to 1.5℃ - the more ambitious of the two targets enshrined in the Paris climate agreement. Last year, global temperatures crossed the 1℃ threshold, and 2016 is on track to be 1.2-1.3℃ above our climate baseline.

But here’s the kicker. That baseline is relative to 1850-1900, when most of our thermometer-based temperature records began. What our study shows is that for many parts of the world that estimate isn’t good enough, because global warming was already under way, so the real baseline would be lower.

The small increases in greenhouse gases during the 19th century had a small effect on Earth’s temperatures, but with the longer perspective we get from our natural climate records we see that big changes occurred. These fractions of a degree of extra warming might seem insignificant at first, but as we nudge ever closer to the 1.5℃ guardrail (and potentially beyond), the past tells us that small changes matter.

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Helen McGregor will be online to answer your questions from 2pm AEST today. Post a query in the comments below.

Helen McGregor, ARC Future Fellow, University of Wollongong; Joelle Gergis, ARC DECRA Climate Research Fellow, School of Earth Sciences, University of Melbourne; Nerilie Abram, QEII Research Fellow, Australian National University, and Steven Phipps, Paleo Ice Sheet Modeller, University of Tasmania

This article was originally published on The Conversation. Read the original article.

What Would Happen if we Abandoned Britain's Farms and Left Them to Nature?

Now what? David Hughes/Shutterstock

by Christopher Sandom, University of Sussex, The Conversation: https://theconversation.com/what-would-happen-if-we-abandoned-britains-farms-and-left-them-to-nature-63951

Without farming, Britain’s countryside would be drastically different. Imagine walking through landscapes un-tilled, un-sown, un-fertilised and un-treated, nor grazed by cattle or sheep.

Following the Brexit vote, the government has to decide what to do about the Common Agricultural Policy (CAP), the EU’s subsidy scheme for owners of farmed land.

Some of these subsidies support food production while others support environmental protection on land suitable to be farmed. In 2015, British farmers received roughly £3.2 billion from the EU.

Agricultural land covers 70% of the UK. If all subsidies stopped, the National Farmers Union reports many farmers would go out of business and large swathes of land would come out of production.

This may be unlikely (and it’s certainly not what I’d recommend) but it’s still worth exploring an even more dramatic scenario: what would happen if Britain’s farmers sold all their livestock and equipment and abandoned their land?

There would be cultural, social and economic shock for sure. With less food grown and reared locally, prices would undoubtedly rise as supermarkets scrambled to secure foreign supply lines. But what would happen to the land itself? Without farming, what would happen to Britain’s nature?

Scenario one: land abandonment

With the hungry mouths of livestock gone, along with the farmer’s ploughs, the great wheels of ecological succession would be freed to turn. Ecological “succession” is the process of change from one set of species to another. In this case, it would begin with dormant seeds, native or otherwise, that would start to emerge. Plants best adapted to fertilised soil such as nettles will thrive.

In time, shrubs and trees will venture into abandoned fields from woodland and hedgerows. Then would come fast growing, light-demanding trees like birch and oak, turning scrubland into early phase woodland. In the shade of the new canopy, lime and elm, both tolerant of low light conditions, will slowly establish themselves until they outlive or outgrow the trees that came before them.

It is a textbook story of succession. The varying climates and soils across Britain mean different species will prosper in different places, and plants will grow at different paces, but in time, in most places, the result will be largely the same. More trees.

England’s green and pleasant lands would mostly look something like this – eventually. ukgardenphotos, CC BY-NC-SA

Herbivores could halt this process in places, and roe, sika and red deer populations would be likely to thrive post-farming. But Britain is missing the heavy-duty herbivores like aurochs (the ancestor of domestic cows) and wild horses that can help halt succession. Storms and fire would open up the canopy in other places, but it is likely that woodland would come to dominate eventually.

So how would this affect Britain’s wildlife more broadly? We can look to the past for insight. Agriculture arrived in Britain around 5,000 years ago. Early farmers cleared woodland to allow them to graze cattle and grow crops. The result of this transition was that plants and animals that favoured open areas thrived. Woodland associated species suffered. In fact, most of the known recent extinctions in Britain are of woodland species, such as the red-backed shrike or scarce dagger moth.

Farmland abandonment would reverse this trend. Species associated with open habitats, such as grey partridge, skylark, lapwing, as well as many bees and butterflies, would find fewer places that meet their needs. But scrub and woodland species, such as bullfinch, nightingale, and capercaillie birds, as well as other groups like moths, beetles, fungi and mammals would thrive once more.

Bullfinches would flourish without farms. f.c.franklin, CC BY-SA

Scenario two: trophic rewilding

What would happen if instead of just abandoning the land, populations of large herbivores such as bison, wild horse, European elk (aka moose) or wild boar were established, along with their predators lynx, wolf and bear?

This scenario is known as “trophic rewilding”. The starting processes would be similar, and succession would still swing into action. But the shrubs and trees trying to establish in fields will be grazed and browsed. Areas of intense grazing would stay open.

But even large herbivores can be less inclined to browse where spiky bushes of bramble, hawthorn and gorse have established. Predators too will mean some areas are relatively free from large plant eaters, who would soon learn to avoid places where they feel at greater risk of being eaten. These plant havens would allow trees to grow, eventually poking out from the protective cocoon of spikes, to emerge above the browsing height of herbivores.

This combination of vegetation-driven processes rising from the bottom of the food-web and predator and herbivore driven processes cascading down from the top can create rich mosaics of habitats. Some of these habitats would be open grasslands full of wildflowers, others mighty woodlands, and some caught in transition. These different habitats would provide for the full range of Britain’s plants and animals.

But, as far as I know, Britain’s farmers have no plans of quitting. Plus, Britain’s nature is well worth investing in to secure our food supply, safeguard biodiversity and restore resilient ecosystems that support society. But this juncture gives us a chance to think about our future and perhaps, in some places, the return of wild nature should be welcomed.

Christopher Sandom, Lecturer in Biology, University of Sussex

This article was originally published on The Conversation. Read the original article.