My father was a bushman before the war.

My father burnt many hectares of ancient native forest.

He burnt the trees down to a hilly grey ashscape. An ashscape littered with black, smouldering stumps and half burnt logs.

In the years before world war 2, my father and his brother worked on their block of native forest in the 'King Country' (as he called it). Day after day they left their homemade 'whare' with their axes and two-man crosscut saws on a mission to "clear the bush". The forest rang to the thud of the axe as they bit notches ('scarfs') into the base of selected forest giants. These scarfs directed where the trees would fall. The two man push-pull crosscut saws severed the trees connection to the earth, and wedges hammered into the cut levered the limb-heavy top over, until, earth-fibres snapping, it tipped, crashing to it's death.

A pit was dug under the fallen tree, and sawing commenced, with my father below (receiving a face full of sawdust on the down-pull stroke - but he was the younger of the two...) and his brother standing atop the trunk. The sawn lumber was dragged out and sold for "3 pence a super foot". Totara is ground durable and splits well, so it was sectioned and split for posts and battens. The fate of the rest of the 'worthless' native forest was to be burned in place. Smaller trees that happened to be more or less in line with the hoped-for direction of fall of the big tree (the 'drive tree') were pre-notched to weaken them and direct their fall, so that the first to be knocked down by the drive tree would in turn knock down the next in line, and so on, like dominos.

The fallen forest would be left for a year or two to dry. Then the fire was set. Once the fierce blaze had died out and the acrid smoke had finally drifted away there was "a five inch layer of ash", my father told me. Whatever native animals survived the destruction of their home became refugees, pushed into remnant forested "gullies", or perhaps a narrow strip of forest left as a windbreak.

Five inches of ash was also five inches of fertility. Five inches of 'free' fertility gave about 5 years before bagged fertiliser had to be applied. Grass seed spread into the warm ash grew lush and strong (and so did the Californian thistles - a common contaminant in the seed in those days). The bigger of the blacked stumps were blown up with a mixture of black gunpowder and sugar. Playing with fire...

Fire destroyed ancient forests; and created pasture. A once-ever natural subsidy. And ryegrass-clover pasture created New Zealand's economic success. With the end of forest ash, our pastoral agriculture took subsidy from phosphate deposits on Christmas Island (mined to extinction), Nauru (mined to extinction), and now is subsidised by phosphate deposits in West Sahara (containing 75% of the world's phosphate reserves, and still being mined - illegally - by Morocco, but not yet extinct).

'Slash and burn' agriculture is practiced today, all around the world. Forests in Malaysia, Borneo, Indonesia are still being burned, mainly to plant palm oil trees. The smoke and pollution is so dense in the 'burning season' that peoples health is affected. Tourists switch to northern Thailand to escape the pollution. In contrast, New Zealand has conserved very large areas of native forest. Other countries are not doing so well.

In a recent paper titled ' Forests, atmospheric water and an uncertain future: the new biology of the global water cycle', Douglas Sheil notes that "over one third of the Earths ice-free land comprises agriculture, pasture and urbanisation", and this  'forest-denuded' area is expanding. He notes that "one and a half million square kilometres of dense tree-cover were lost between 2000 and 2012".

That statistic - one and a half million square kilometres of dense tree-cover - is very hard to visualise. Imagine the entire of the South Island of New Zealand was covered in dense forest (no cities farms etc). Coast to coast. Now chop it all down, Bluff to Nelson. That is the picture. And all in 12 years. But that is not a one-off event. It is a continuing process.

This graphic of forest loss in the Amazon is more powerful than images conjured up by words alone:

The looped videos in this @qz story show how indigenous reserves are vital for protecting Amazon rainforest in a way that words never couldhttps://t.co/DNmf5lYthd pic.twitter.com/YsmuMfi5PN

Peter Aldhous (@paldhous) November 1, 2018

Forests and climate are an intimately linked system.

"Global vegetation and climate are linked in both directions: when climate changes, so will vegetation, and when vegetation changes, so will the climate. These links are more important, more complex, and more poorly characterised than most people realise." - Douglas Sheil

Well, vegetation in New Zealand and around the world has certainly changed. According to Douglas Sheil this must lead to changes in climate, although the nature of the changes are uncertain. He notes that the global water-cycle is still one of the least understood natural cycles. The interaction of water on the land - water bodies, water in soil, transpired by plants etc - and the interaction with atmospheric water is complex and poorly understood.

Changing climate has the effect of melting frozen water stores in permafrost, glaciers, ice caps and sea ice. What effect these changes have on atmospheric moisture, the formation of clouds, precipitation (rain or snow) and the water cycle are full of uncertainty. But the effects of atmospheric moisture patterns and reliability, from a human perspective, are of intense concern. Snowpack supplies water to cities. Monsoons are the guarantors of harvests, the givers of life. Winter rains recharge underground artesian water stores. Summer rains can ruin grains that were dry and ready for harvest. Half a billion people endure scarce water supplies all year long, and two-thirds of the worlds people have insufficient water for more than a month in a year. Recent tree ring data that show that periods of severe drought in parts of western Mediterranean are within the range of natural variability occurring over the last 900 years, but the drought in Syria, and in some other parts of the eastern Mediterranean, is the worst in 500 years. The Syrian drought falls outside the range of expected variation for the 900 year period studied - suggesting a shift in the local hydrological cycle. Examples of such vulnerabilities and uncertainties are endless - and endlessly important.

Perhaps most important is change in atmospheric water vapour, because water vapour is the dominant greenhouse gas, trapping heat, warming air, allowing more water vapour to be held, and therefore heavier rain to fall. This can be an amplifying feedback loop in areas surrounded by large bodies of water. Models predict water in the atmosphere will increase by 7% for each degree Celsius of surface warming, and experience so far shows precipitation increases at roughly the same rate.

Almost 40% of the rain and snow that falls on land comes from water, but 60% of rain and snow is water recycled from land. Water vapor from large scale forests, such as the Amazon, East African forests, the temperate forests of Western North America, and the massive forests of Central Eurasia can travel downwind in the atmosphere for up to 500 kilometers (typically) to 5,000 kilometers (less frequently) before falling as rain. So global warming means more water vapour can be held by air over water, but in some areas, de-forestation might mean less water vapor being pumped into the atmosphere over land.

Tree death in the Sierra Nevada, California (yellow, left map), can reduce water to the atmosphere, reducing vegetation growth across the continent (brown, right map). Research by Abigail Swann @ecoclimatelab, @davebreshears, in @iopenvironment https://t.co/XxBXUN4GGk pic.twitter.com/kXRLWymbPc

Patrick Gonzalez (@pgonzaleztweet) June 2, 2018

Stocks and flows and uncertainty

"The structure of a system is its interlocking stocks, flows, and feedback loops...Systems fool us by presenting themselves - or we fool ourselves by seeing the world - as a series of events. Much of our ordinary conversation is about specific happenings at specific times and places. A team wins. A river floods...A forest is cut. Events are the outputs, moment by moment, from the black box of the system...Its endlessly engrossing to take in the world as a series of events, and constantly suprising, because that way of seeing the world has almost no predictive or explanatory value ...long-term behaviour [of the system] provides clues to the underlying systems structure. And structure is the key to understand not just what is happening, but why." Systems Analyst Donella Meadows

Donella Meadows observes that most attempts to explain what is happenng in the world is simply a superficial opinion on events. A slightly deeper analysis looks at the motives for the behaviours of the actors. Deeper analysis looks at the current flows of stocks (she gives the example of flow of goods and services at any point in time) rather than the stock (physical capacity of factories and farms, physical supply and limits of capital stock of raw materials etc). This simplistic superficial linear thinking - 'well, this will lead to that, and then probably to that' - assumes no complexity, let alone accounts for rare but 'game-changing'events. Linear thinking cannot even conceive of feedbacks coming from other ignored parts of a complex dynamic system. A system might tend to be self-balancing, with a bad effect tending to be cancelled by a good effect, or it could be at some point in developing a 'runaway' self-reinforcing feedback loop. It is easy to understand a runaway self-amplifying feedback loop when it is an immediate event - Fukushima nuclear power plant disaster is a good example - but much harder when it is a slow and constantly micro-varying trend - like human 'forced' climate change. The main root cause of climate shift is carbon dioxide increase.

Let there be no doubt about it - there are two 'stocks' of carbon that are being burned to form carbon dioxide, one harmless, the other deadly.

Put simplistically, one stock is the 'body' of all the plants on earth. Carbon dioxide 'flows' from this stock when forests are burnt, or the trees fall and rot. But under a 'natural' system, any time a tree falls another seedling takes it's place in the sunny gap in the dense forest canopy. Soon the gap closes again, and the tree that grows to close the gap takes carbon dioxide out of the atmosphere to build its body. Death and new life balance to nett no gain or loss of atmospheric carbon dioxide. Man-made or natural, the 'flow' of growth, removal, and replanting of forests are more or less carbon nett neutral in the 'natural system' stock.

The other stock is the buried ancient geological stock, primarily the coal, crystalline carbon. It should never ever be drawn on. It should remain buried forever. This stock should never have been allowed to 'flow' into the atmosphere. Unlike the 'natural' stock, the ancient carbon dioxide released from burning coal cannot be re-buried.

Planting more trees does not help.

First, the trees will be cut and eventually rot, releasing carbon dioxide. Storage, in other words, is only temporary.

Second, extra tree planting is not even compensating for the South Island's worth of trees being destroyed every ten years or so, let alone re-sequestering ancient carbon dioxide that should never have been released from its deep underground tombs.

This bad situation continues to be made worse. For example, forests continue to be cut in Pakistan even while coal production from the Thar coalfields in eastern Sindh is due to start next year (2019). The Thar coalfield contains about 175 billion metric tons of coal. A metric tonne of coal creates 3 - 5 tonnes of carbon dioxide (depending on carbon content).

The only way to pull this ancient carbon dioxide back out of circulation is to re-create coal. That is, wait for a warm and wet global hydrological condition, don't drain the resultant ever-expanding swamps, let vegetation fall into the waters and rot, let heavy rain wash silt onto the layers of carbon-containing vegetation, let earthquakes drop some of these swamps under the earth, compress for millions of years until heat and pressure form crystalline carbon (coal), and bingo! Success!

My Take Home Message

Of course, if the human footprint is reduced; if there is a massive global effort to abandon coal; if there is massive re-forestation; and if we do a million small things to use renewable energy and re-green, well, there might be a chance.

"...the Paris Agreement on Climate Change, the United Nations is pursuing efforts to limit global warming to 1.5C, whereas earlier aspirations focused on a 2C limit.
With current pledges, corresponding to [about] 3.2C warming, climatically determined geographic range losses of >50% are projected in ~49% of insects, 44% of plants, and 26% of vertebrates.
At 2C, this falls to 18% of insects, 16% of plants, and 8% of vertebrates and at 1.5C, to 6% of insects, 8% of plants, and 4% of vertebrates.
When warming is limited to 1.5C as compared with 2C, numbers of species projected to lose >50% of their range are reduced by ~66% in insects and by ~50% in plants and vertebrates."

- Warren et al, 2018. 'The projected effect on insects, vertebrates, and plants of limiting global warming to 1.5C rather than 2C' Science, Vol. 360, Issue 6390, pp. 791-795

There is no chance average global warming will be limited to 1.5oC.

Putting money on at least 3oC warming is a pretty safe bet.

Either we choose to stop releasing stocks of ancient carbon dioxide now, or the remnant population living in the still habitable parts of the planet will have so few energy requirements it won't matter.

Douglas Sheil Take Home Message

"Among the most profound and disturbing insights  offered by this review is the potential for non-linear behaviours: the indication that a continent or region that passes some threshold of forest loss might tip from a wet to a dry climate. While various details remain poorly characterised, and some are debated, the overall linkages appear uncontroversial. We know that large  scale  forest  loss  or  die-back  will  generally reduce atmospheric moisture, rainfall and cloud cover, and increase the likelihood of drought and further loss or die-back. Add in human activities, increasing temperatures and fires, and changes could be rapid, making whole regions near uninhabitable and releasing vast amounts of carbon stored in vegetation and soils into the atmosphere over only a few years. There is also a positive side: rainfall can be stabilised and regained by maintaining and restoring tree cover. Characterising these threats and opportunities is a priority."

Read much, much more at:
http://www.cifnor.org/publications/pdf_files/articles/ASheil1801.pdf
Douglas Sheil, 'Forests, atmospheric water and an uncertain future: the new biology of the global water cycle'.