By 2100 earth will warm between 1.4° and 5.8° C (2.52° to 10.44° F) according to the Intergovernmental Panel on Climate Change (IPCC). Although this sounds like a sunny and pleasant upside to vacation weather forecasts, as "Six Degrees Our Future on a Hotter Planet" by Mark Lynas soberly notes, the consequences range from the inconvenient to the inconceivable as massive rockslides reshape the Alps, atoll nations across the Pacific are inundated, species extinction accelerates, and entire ecosystems collapse. The web of life - humanity's safety net - will disappear, stranding us on an essentially alien planet.
Denialism invites devastation on a scale last seen during the Permian-Triassic (P-Tr) extinction event, and business or politics as usual will impose surrogate suicide on our children and grandchildren. Degree by degree "Six Degrees" explains the mechanisms behind global warming and the direct consequences of our actions (or inactions). From sophisticated and increasingly refined computer models, to the latest geological and paleontological evidence, Lynas compellingly argues that anthropomorphic climate change is a new and unprecedented challenge verging on calamity, not a routine and recurrent phenomenon due to cyclical natural causes.
From bleached and dying tropical coral reefs to polar bears that will melt into history along with the glaciers and ice flows they called home, the future is dire unless immediate, but achievable steps are taken. Some species may survive by migrating, but most will have nowhere to migrate to. Small changes result in sizeable impacts - a mere 3° C increase will turn the American Midwest, the world's breadbasket, and the Amazon Basin which supplies 20% of earth's fresh water, into arid wasteland.
Deluge or desertification will erase entire countries from the map and displace massive populations, as former citizens become stateless refugees. New York, London, Bombay, and Shanghai could be lost to the sea. Unless we redesign our energy extravagant carbon culture in less than a decade, reversion to pre-industrial civilization, or even a second stone age, may be our inevitable legacy.
At 1° C the American West, from California to the Great Plains could suffer a mega-drought lasting decades or centuries - devastating agriculture and evicting inhabitants on a scale far larger then the 1930s dustbowl. Overexploited aquifers will fail as powerful dust and sandstorms engulf entire states. Although more southerly parts of the United States are expected to get wetter as the North American monsoon intensifies, residents may not welcome an influx of several million eco-refugees. Europe, Africa, the Middle East, Asia, and Australia will face similar challenges.
Plus 2° C will bring thirst to parched cities across China. Facing a chronic shortage of water, China won't struggle to develop a more affluent lifestyle; it will fight to feed itself. Warmer seas will continue - less efficiency - to absorb additional greenhouse gas emissions, radically altering the interlocking and exquisitely balanced ecosystems that cover 70 % of the globe. At least half the carbon dioxide released by airliners, air conditioners, or anything else ends up in the sea - a naturally alkaline environment that allows diverse and vital organisms to build calcium carbonate shells.
Human activities have already reduced oceanic alkalinity by 0.1 pH units. In less than 100 years the pH of the oceans could drop by half a unit from its natural 8.2 to about 7.7 - a change that will severely impact plankton - the foundation of coastal or deep water food chains. Although individually tiny (only a few thousandths of a millimeter across), photosynthesizing plankton like coccolithopores are arguably the most important plant resource on earth. They comprise at least half the biosphere's entire primary production - equivalent to all land plants combined. When scientists simulated anticipated future pH levels by pumping dissolved carbon dioxide into a Norwegian fjord, they watched in dismay as coccolithopore structures corroded and then disintegrated altogether.
Gourmets will morn the loss of mussels, scallops and oysters, shellfish vitally important as economic resources and constituents of coastal ecosystems worldwide, as they loose their ability to build strong shells by the century's end - and will dissolve altogether if atmospheric carbon dioxide levels reach 1,800 ppm. Gastric distress of a different sort will follow as fisheries collapse and dependent populations face famine. Walk on a coral reef in 2090 and it could crumble beneath your feet. The haphazard experiment we are conducting on the world's oceans is insanely irresponsible.
Europe will experience temperatures endemic to North Africa today by 2040 and the consequent death toll during searing summer heat waves may reach into the hundreds of thousands. Mediterranean sunburn will take on an entirely new connotation in a 2° C world.
Adding 3° C will see a return to Pliocene norms (5.3 to 1.8 MYA) - when the Transantarctic Mountains were covered with beech trees, admittedly stunted by harsh conditions, but thriving. Pine trees will return to regions hundreds of miles north of today's artic tree line, and global sea levels will rise 25 meters (27.34 yards). Other harbingers include a persistent super El Nino, desiccation of the Amazon and Australia, hyper-hurricanes (Houston, we have a problem), an ice-free arctic, dry Indus and Colorado rivers, and the inundation of New York City.
Growing food in this hotspot habitat will prove increasingly problematic since rice, wheat, and maize yields decline by 10% for every 1° C temperature increase over 30° C. Over 40° C yields are reduced to zero. Starvation will replace obesity as an epidemic, and genetically modified organisms (GMOs) will be our only alternative.
An additional 4° C will see the end of the Nile and Egyptian civilization; although Alexandria will be flooded as Antarctic ice melts raise global sea levels by 50 meters (164.1 feet). If both major Antarctic ice sheets destabilize sea levels could rise by a meter or so every 20 years - far outside humanity's adaptive capacity. Global warming of this magnitude would eventually denude the entire planet of ice for the first time in nearly 40 million years.
With 5° C of global warming a new planet, unrecognizable and indifferent to the needs of humanity arrives. Rain forests have burned up and rapidly rising sea levels, after inundating coastal cities, are beginning to penetrate far inland into continental interiors. Humanity will be confined to precarious habitability zones delineated by the twin scourges of drought and flood. At the highest latitudes Siberian, Canadian, and Alaskan rivers will experience dramatically increased flows due to torrential rain. A resurgent East Asian monsoon will dump nearly a third more water in the Yangtze, nearly 20% more in the Huang He (Yellow River), and the United Kingdom will experience severe winter flooding as reset Atlantic weather patterns lash Britain, Scotland and Ireland with Noachian (for lack of a better term) ferocity.
Globally, our planet will reprise conditions last experienced during the Paleocene-Eocene Thermal Maximum (PETM). Nearly every academic PETM study published in recent years notes that this epoch presages what anthropogenic global warming might have in store. Although the total carbon dioxide input into the atmosphere 55 MYA exceeded our best efforts to date - with carbon dioxide levels of more than 1,000 ppm persisting into the early Eocene - the rate of greenhouse gas addition is actually faster in the early Anthropocene (today) than during the PETM event.
Disruption on this scale could unleash massive amounts of methane hydrates (methane is an even more potent greenhouse gas than carbon dioxide), resulting in runaway global warming. Humans would watch powerlessly as their planet began to emulate Venus. How likely is this scenario? A recent study by methane hydrate experts, Bruce Buffet and David Archer, suggests that the store of hydrates on the ocean floor would decrease by 85% in response to just three degrees of warming - although they don't say how long this shift might take. Is that shiny new SUV or humongous Hummer really worth the risk to your children and grandchildren?
In some ways, a return to Eocene norms seems Edenic. Lush forests grew at the poles, temperate zones became subtropical, and fascinating species spread across the globe - but the PETM took place over approximately 10,000 years, giving plants and animals time to migrate and adapt to new circumstances. We don't have 100 centuries - only decades - a pace of warming far too rapid for meaningful adaptation by natural ecosystems or human civilization. Humanity will become an endangered species.
Channeling Dante as our guide to a 6° C increase is warranted as earth descends into the Sixth Circle of Hell. Welcome to 'Cretaceous Park' (144 - 65 MYA) without the tourist attractions as a best-case scenario, or the Permian-Triassic (P-Tr) extinction event (251 MYA, also known as the Great Dying) - when life itself nearly died - as the worst-case outcome. Peter Ward's superb Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us About Our Future (reviewed separately, an excellent companion book) documents how rampant greenhouse warming triggered anoxic oceans to release massive amounts of poisonous hydrogen sulfide (rotten egg gas) into the atmosphere. Oxygen levels plunged to 15% (contemporary levels are 21%) and many organisms (terrestrial and oceanic) literally suffocated.
Lynas points out that we can still choose our future - but unless we act to reduce greenhouse gas emissions within just a few years our destiny will be chosen, and earthly inferno will become inevitable as carbon cycle feedbacks and climate forcings kick in one after another. We have the technology, but do we have the collective will?
"Six Degrees" is a tour de force that deserves to be widely read and acted upon. Until politicians act, take action. Lynas has also published The Carbon Calculator, which outlines easy ways to reduce your carbon footprint, before we become just another failed species marked by fossilized tracks on the margins of a long evaporated lake.
Other excellent books on global warming include Storm World: Hurricanes, Politics, and the Battle Over Global Warming by Chris Mooney, With Speed and Violence: Why Scientists Fear Tipping Points in Climate Change by Fred Pearce, and Field Notes from a Catastrophe: Man, Nature, and Climate Change by Elizabeth Kolbert.