Global climate changes tend to be abrupt. And they could also become irreversible.

The most recent scientific report on this issue is from the the US Climate Science Program...

Abrupt climate change is defined as a large-scale change in the climate system that takes place over a few decades or less, persists (or is anticipated to persist) for at least a few decades, and causes substantial disruptions in human and natural systems. Four types of abrupt change in the geologic record stand out as being so rapid and large in their impact that, if they were to recur, they would pose clear risks to society in terms of our ability to adapt:

• Rapid change in glaciers, ice sheets, and hence sea level.
• Widespread and sustained changes to the hydrologic cycle, including drought and flooding.
• Abrupt change in the Atlantic Meridional Overturning Circulation, a critical component of global climate, characterized by the northward flow of warm, salty water in the upper layers of the Atlantic Ocean.
• Rapid release to the atmosphere of methane, a powerful greenhouse gas, trapped in permafrost and in ocean sediments.

The text of the report includes another very important type of abrupt change—permanent drought.

Climate model studies over North America and the global subtropics indicate that subtropical drying will likely intensify and persist in the future due to greenhouse warming. This drying is predicted to move northward into the southwestern United States. If the model results are correct, then the southwestern United States may be beginning an abrupt period of increased drought.

You can read the report here.

The 2002 Abrupt Climate Report by the National Research Council (US) Committee on Abrupt Climate Change is online in full and is still a must read. From its first page...

Recent scientific evidence shows that major and widespread climate changes have occurred with startling speed. For example roughly half of the north Atlantic warming since the last ice age was achieved in just a decade....

Similar events including local warmings as large as 16° C occurred repeatedly during the climb into and the slide out of the last ice age.

Severe droughts... during the current warm period have shown similar tendencies of abrupt onset and great persistence....

The term used most often in reference to catastrophic global climate change is "tipping points." The slippery slope analogy is more in keeping with the science.

Global warming results in the planet being hyper-energized.

Industrial atmospheric greenhouse gas pollution has put the systems of the planet out of energy balance on a down hill course.

The tipping point analogy is dangerous. It assumes that at some stage any of the systems will pass a tipping point, past which anything that humans can do will not make the slightest difference. But natural systems do not work like that. They have elasticity. They adjust to maintain equilibrium until at some point they snap and suddenly collapse to a new lower level of equilibrium.

Cascading tipping points are known as a planetary domino effect, where one collapse triggers the next, which triggers the next, and so on...

The one described by James Hansen et al. in their Planet is in Imminent Peril 2007 paper relates to the Arctic. The paper warned that the meltdown of the summer Arctic Ocean ice could start a chain reaction leading to a planetary cataclysm. We have gone too far on the Arctic slippery slope of global warming already.

Various regions of the planet would suffer irreversible damage, rendering them practically uninhabitable by humans and other species.

The capacity of atmospheric greenhouse pollution to cause irreversible damage to the planet is what makes global climate change catastrophic to an extent that humanity has never before had to face. The reason for that is "tipping points" (see below).

Today's atmospheric greenhouse gas levels do not correlate with today's increased temperature level. The surface of the planet is mostly composed of ocean water. Water takes a long time to heat, but it then holds that heat in for a very long time. Since it takes several decades for a greenhouse gas emission's effect to register in the planet's overall temperature. This delay is called the heat/thermal lag. All future generations are committed (condemned) to a global warming of over double our warming today.

We should be basing assessments on today's atmospheric carbon concentrations and their total (including future) warming effect.

As Earth's carbon sinks (our oceans and forests) fill up, less carbon dioxide can be absorbed by them. For example, warmer ocean water can hold less carbon dioxide. This is a positive feedback loop, where warming water means less carbon dioxide absorption, which means more global warming, which means less absorption by our oceans.

Even worse, a far greater positive feedback loop between warming and the thawing permafrost of northern Canada and Siberia (which currently hold massive amounts of carbon in the form of methane) is developing.

This will result in more methane (much more potent at holding in heat) being released into the atmosphere, which will further heat it, which will further thaw the permafrost, releasing more methane, which will...

Unfortunately, the world is already condemned to these catastrophic climate change impacts to global ecosystems, biodiversity, global agriculture and huge human populations. The scientific opinion today is that a global warming of 2° C is practically impossible to avoid.

The fact we must face is that we have imminent and unavoidable catastrophe happening at today's global warming of 0.78°C. At a global warming of 0.78° C, all planetary ice masses are melting.

The melting of the Greenland icesheet and South American and Himalayan glaciers is accelerating. The melting of Arctic Ocean ice is accelerating. These are all catastrophic because it is now impossible to stop the melting, which can only continue to accelerate.

The current policy of 2° C is certain catastrophe, and this is still not being acknowledged.

The 2° C limit was a European Union policy danger limit of many years ago. It was based on the assumption that above 2° C, carbon feedbacks would provide an unacceptable risk of runaway global heating. The European Union admits 2° C is not a safe limit. These carbon feedbacks are happening now at today's global warming of 0.78° C.

If the climate scientists do not advise governments that the current policy of targeting 2° C as the safe limit is a policy for global catastrophe, then the worst possible impacts are assured. We know that 2° C is certain catastrophe because of the planetary melt down of ice masses happening today at a global warming of 0.78° C.

Climate change scientists, referring to the worst impacts of global climate change to be prevented, go by the massive geophysical catastrophe definition of "a violent and sudden change in a feature of the Earth" (Webster Dictionary).

The scientists focus on the meltdown of the Greenland ice sheet and of Antarctica, leading to a global rise in sea level and inundation of coastal cities. This makes for great computer graphics and debate about how far the sea level could rise, but it is practically irrelevant.

Human civilization would have collapsed long before the catastrophic rise in sea levels from a combination of climate changes that are now imminent.

Focusing on sea level rise as the danger to avoid is like the Captain of the Titanic's policy on safety in the foggy north Atlantic. When warned repeatedly by other ships that the foggy north Atlantic waters the Titanic was on course for contained icebergs and the course should be changed, he told his crew to go full steam ahead and look out for icebergs. The lookouts reported the iceberg as soon as they saw it.

A more relevant definition of global climate catastrophe for us would be by the general commonsense understanding of a "momentous event"—"leading to ruin" (Webster Dictionary).

Incredible as it is, climate change scientists and the policy makers have no agreement on how dangerous, disastrous or catastrophic global climate change is, or how it should be defined. The only agreement is that it refers to greenhouse gas levels.

The scientists and policy makers do not even have an agreed safe limit on the level of global warming. They go along with the so-called 2° C danger limit but this is a policy proposal and has no basis in science as a limit. It is certainly catastrophically dangerous. Nevertheless, it has now become a target.

Both groups say that the FCCC does not define dangerous climate interference, which is simply not true and indicates they can not have read the full convention.

This only serves to increase the risk of catastrophe because the key obligation on nations by the 1992 UN FCCC is the avoidance of "dangerous interference with the climate system."

Catastrophic climate change is what will certainly happen by not taking measures to avoid dangerous interference, which means avoiding concentrations of atmospheric carbon emissions. That is exactly what we are doing. So far the world has not taken any such measures and there are no plans for such measures.

The result of scientists and nations discussing what "dangerous" means and doing nothing to avoid it is that global greenhouse gas emissions have pushed atmospheric concentrations far above the safe limit and into the catastrophic danger zone.

The sooner this is acknowledged, the better chance there is for some political will to develop that would see global emissions fall. Today emissions are at a record high, above the worst case scenario of the climate change scientists.

The sooner the truth is faced, the less severe may be the catastrophic impacts and the safer the planet might be made for today's children.

The atmospheric levels of greenhouse gases have been allowed to rise to such extremely high concentrations (and are still accelerating) that planet Earth can no longer be assumed to remain a safe place for humanity. The planet will be damaged as IPCC co-chair Prof Martin Parry said when delivering the impacts report of the IPCC assessment in 2007.

The two single most catastrophic global climate change dangers are to agriculture and from Arctic carbon feedbacks loops.

Neither is acknowledged by the IPCC assessment nor recognized as such by the current UN FCCC negotiations. The IPCC excluded all carbon feedbacks from the Panel's assessment!

The global warming and climate disruption impacts on agriculture are the greatest danger for the survival of human populations, civilization and humanity. Although an increase of carbon dioxide boosts the growth of green plants, global warming and climate disruption are disastrous to agriculture. The main reasons are simple...

• Global warming increases climate variability. Moderate, predictable climate is the first essential for agriculture.
• Crops can withstand only a limited amount of heat and drying.
• Crops fail with insufficient water.
• Storms and floods damage food crops.

As the Arctic thaws, the region will release additional carbon dioxide and methane into the atmosphere, which, if emitted fast enough, will lead to irreversible runaway global heating and abrupt (within just a decade or two) global climate change.

There are obvious climate change situations that are catastrophic by common sense and have to be avoided at all costs...

• Pandemics of global warming and climate change-induced diseases.
• Regional and global collapse of agriculture.
• Civilization's collapse due to the collapse of agriculture.
• Humanity's collapse, returning to Stone Age conditions with only the survival of remnant isolated populations.
• The collapse of life in the oceans from acidification and warming.
• The extinction of most life on Earth.

Climate change scientists and policy makers say that they can't tell us what is dangerous, but any atmospheric concentration of greenhouse gases that are not known to be safe must be assumed to be dangerous and avoided.

All of the discussion above looks only at the effect of global climate change in isolation.

One of the serious problems with the way that global climate change is being assessed is that it's being done by an extremely reductionist approach to the science. Scientists refuse to consider that the impacts estimated by the IPCC are on top of many ongoing global environmental and socioeconomic changes.

The truth is that another group of scientists first told us we have been living in a planetary catastrophe, of our own making, ten years ago. We are in the sixth mass extinction of life on Earth, and it's already happening faster than the natural catastrophes of the far distant past.

Industrial scale deforestation and ecosystem degradation by urban sprawl and highways is the cause of this mass extinction. Biologists estimate the rate at between 100 to 1,000 times the natural background of species extinctions.

When we read that global climate change will cause the extinction of 30% of the planet's species, the truth is that it will cause an additional 30% more extinctions. The leading biologists like Edward O. Wilson and Peter Raven estimate that 60% of all species will be doomed to extinction by the end of the 21^st century by the direct habitat factor.

The same process applies to human catastrophes...

• 1.1 billion people live without clean drinking water.
• 2.6 billion people lack adequate sanitation (UNICEF 2002/WHO JMP 2004).
• 1.8 million people die every year from diarrheal diseases.
• 3,900 children die every day from water-borne diseases (WHO 2004).
http://www.worldwatercouncil.org/index.php?id=25

The IPCC assessment estimated that between one and three billion people will be impacted by water scarcity due to climate change by 2100. The UN Development Program 2007 report, Fighting Climate Change: Human solidarity in a divided world, reported that an additional 1.8 billion people will face water stress by 2080. The third UN World Water Development Report, Water in a Changing World, on March 16 2009 reported the full truth.

According to the most recent forecasts, in 2030, 47% of Earth's population will live in water-stressed areas, and 67% will not have access to sanitation. That's at least 4 billion people without either sufficient water or clean water.

For information about other aspects of our looming climate catastrophe, click on any of the red buttons on the left. Or click on a green button to learn about the only option we have to save ourselves—the zero carbon economy.