Climate Change represents the greatest single adaptation humans will hopefully not have to make over the next century. What is disturbing is that ongoing observations are exceeding worst-case scenario climate model projections made not so long ago. All roads seem to be leading to the question over how long before we reach a point at which we can no longer prevent a cascading series of feedback loops that set Earth's climate at a new equilibrium. Is it 350 ppm of CO2 in the atmosphere? Is it 2C (3.6F) rise in global average temperature? Something else?
Currently we are at about 390 ppm CO2. In pre-industrial times, that number was 280. So we are experimenting with what happens when we add 40% more carbon and on our way to doubling it from pre-industrial levels well before the end of the century unless something is done to stop it. A doubling is certain to cause a catastrophic climate shift upwards of 5C (9F) or more, depending on where these trigger points lie. The current thinking is that a major trigger point could well be at 2C judging from the rapidity of the ice melt in the Artic and mountain glaciers with only a .8C temperature rise so far. What is feared is that, as the Artic Ocean turns to open water during the summer months, the albedo effect will cause runaway ocean water temperature rise that will in turn melt Greenland's massive ice sheet into the North Atlantic. In addition to this, because the blue ocean water absorbs more solar radiation and therefore more heat than ice does, that additional heat will contribute to further global temperature rise generally. It goes without saying that we could not stop this source of warming.
What the trigger point(s) mean is that, upon reaching 2C above pre-industrial levels, a rise to 5C above pre-industrial levels would be more or less automatic. That is a probable equilibrium point for global climate. In the absence of additional major trigger points then that is likely where it would stay for thousands of years until the CO2 gets reabsorbed into natural carbon sinks like ocean water and plant life.
It is really beyond dispute among reasonable people that the temperature rise is caused by the burning of fossil fuels to power human economic activity. Those who say otherwise are saying so for economic or ideological reasons, and not for scientific ones. It is known well enough what impact increased CO2 has in the atmosphere. This particular property of CO2 (letting in solar radiation but absorbing heat radiation rising from the surface of the Earth) has been known since the 19th century. What is unknown are the particulars of how much carbon does what, or what other factors might exacerbate or mitigate the carbon effect. At some point I will write a post on the difference between skepticism and denial and demonstrate why the time for skepticism is over for climate change. Those who continue to question the veracity of anthropogenic global warming are denialists.
The widest scale on which to view the magnitude of our climate situation is to consider the following: the past 11,000 years, known as the holocene, have been the most stable climatic period in the history of the Earth. It just so happens to correspond to the period in which civilization has grown up. We cannot know how a climate shift northwards of 2C will have on every little piece of territory around the globe and how we could manage with the unpredictable weather that would come along with it. What we do know is that the hydrological cycles around the globe will be disrupted, with deserts expanding into places where food is now grown. We know that disappearing glaciers will have a devastating effect on agriculture in many of the most populated regions of the world. We know that increased CO2 concentrations in the air will increase it in the oceans, making the ocean water more acidic and harm and force into extinction a wide range of ocean species. Finally, we know that ocean levels are rising and will rise further as land ice from Greenland and Antarctica melt into the ocean, inundating coastal cities. All of the above is observable and measurable now. The rates are increasing.
As if this isn't enough, there is growing evidence that the amount of warming that should be happening from rising CO2 levels is being masked by the diminishment of sunlight striking the Earth due to the particulate matter and aerosols that come with the burning of fossil fuels. One study has estimated the amount of sunlight reflected back into space is reducing the amount of warming by 30-50%. Now, this is only one study but there are sure to be more. If true, and you couple this with the amount of carbon in the pipeline that has not yet caused warming, then we are already about 3/4 of the way to 2C.
It's clear that humanity needs to work quickly to get to zero carbon emissions if we want to have a climate that resembles that of the holocene period. If we fail to do this, then we will have ended the stable, nurturing holocene and entered a new and dangerously unpredictable anthropocene period. And I am only occasionally given to hyperbole. This is not one of those times.
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