(Global carbon emissions continued along a worst-case track during 2013. Note that estimated temperature increases are for this century only. For context, it took 12,000 years for the world to warm 5 degrees Celsius at the end of the last ice age. Image source: Global Carbon Project.) On the current track, global CO2 emissions will double in about 30 years. This pace of emissions increase is along the worst-case path projected by the UN’s IPCC. One that will hit 8.5 watts per meter squared of additional warming at the top of the Earth’s atmosphere and greater than 1,000 ppm CO2 equivalent greenhouse gas heat forcing by the end of this century. Such a massive increase from human sources does not include amplifying feedback emissions from global methane or CO2 stores such as those now apparently destabilizing in the Arctic. Such emissions could add an additional 20 to 30 percent or greater heat forcing on top of the human forcing, according to scientific estimates, by the end of this century. The massive blow would be more than enough to trigger a hothouse extinction event — one that could well rival or exceed the Permian (also known as ‘the great dying’) in its ferocity due to the very rapid pace of the human heat accumulation.

The oceans have a huge thermal mass compared to the atmosphere and land surface. They act as the planet’s heat storage and transportation system, as the ocean currents redistribute the heat. This is important because if we look at the global surface temperature as an indication of warming, we’re only getting some of the picture. The oceans act as a huge storage heater, and will continue to warm up the lower atmosphere (no matter what changes we make to the atmosphere in the future).

The percentages were calculated from Figure 5.4 from Section 5.2.2.3 of the IPCC 4th Assessment Report (h/t to Humanity Rules for the heads up). The IPCC graph shows changes in energy content for two different periods: 1961 to 2003 and 1993 to 2003. The ocean heat figure of 93.4% is almost certainly an underestimate as it only includes ocean heat down to 700 metres (Levitus 2005).

Accelerated Warming The second thing to fear about loss of Arctic sea ice is the potential to accelerate climate change on a global basis. A black object gets hotter in the sun than a white object. That much is common sense. Earlier, in describing how melting ice accelerated the melt of more ice, I talked about the fact that dark sea waters absorb up to 90% of the sun’s energy that strikes them, while snow-covered ice absorbs only 10 to 20% of that same energy. The exposure of darker waters speeds up heating of the Arctic, and thus the loss of more ice. But the impact is larger than that. And indeed, it’s large enough to make a difference on a global scale. In June, the Arctic ice cap covers around 2% of the Earth’s surface – around 11 million square kilometers of Arctic ice cap out of a total of 510 million square kilometers of Earth’s land and oceans. And that 2% of the Earth’s surface, for a period of roughly two months, receives more solar energy per day than even the sunniest areas on the equator. Analyzing this, Peter Wadhams of the Global Oceans Physics Program at Cambridge calculates that the loss of the Arctic ice throughout the summer would have a warming effect roughly equivalent to all human activity to date. That is to say, with the ice gone in summer, the planet would have an additional heating effect just as large as the heating effect of all human CO2 and other greenhouse gasses to date. In other words, the complete meltdown of the Arctic could roughly double the rate of warming of the planet as a whole.

Figure 2.29. Model simulations of Arctic sea ice extent for September (1900-2100)
based on observed concentrations of heat-trapping gases and particles (through
2005) and four scenarios. Colored lines for RCP scenarios are model averages
(CMIP5) and lighter shades of the line colors denote ranges among models for
each scenario. Dotted gray line and gray shading denotes average and range of
the historical simulations through 2005. The thick black line shows observed data
for 1953-2012. These newer model (CMIP5) simulations project more rapid sea ice
loss compared to the previous generation of models (CMIP3) under similar forcing
scenarios, although the simulated September ice losses under all scenarios still
lag the observed loss of the past decade. Extrapolation of the present observed
trend suggests an essentially ice-free Arctic in summer before mid-century.139 The
Arctic is considered essentially ice-free when the areal extent of ice is less than
one million square kilometers. (Figure source: adapted from Stroeve et al. 2012136).

Up to a 2 degree C increase, the expected sea level rise is about 10 meters per degree C (8 feet per degree F)

There's not as much polarization among experts as you might think. The chart below comes from Stefan Rahmstorf, one of the authors of the paper. He notes over at Real Climate that there aren't two wildly opposing "camps" of sea-level experts, as press accounts have sometimes suggested.

Flooding during high tides—something that rarely occurred in the past—is now common in some places and is projected to grow to the point that sections of coastal cities may flood so often they would become unusable in the near future, according to a report the Union of Concerned Scientists (UCS) released today, “Encroaching Tides: How Sea Level Rise and Tidal Flooding Threaten U.S. East and Gulf Coast Communities over the Next 30 Years.”

As human-induced emissions of carbon dioxide (CO2) build up in the atmosphere, excess CO2 is dissolving into the oceans where it reacts with seawater to form carbonic acid, lowering ocean pH levels (“acidification”) and threatening a number of marine ecosystems. Currently, the oceans absorbs about a quarter of the CO2 humans produce every year. Over the last 250 years, the oceans have absorbed 560 billion tons of CO2, increasing the acidity of surface waters by 30%.,, Although the average oceanic pH can vary on interglacial timescales, the current observed rate of change is roughly 50 times faster than known historical change., Regional factors such as coastal upwelling, changes in discharge rates from rivers and glaciers, sea ice loss, and urbanization have created “ocean acidification hotspots” where changes are occurring at even faster rates. The acidification of the oceans has already caused a suppression of carbonate ion concentrations that are critical for marine calcifying animals such as corals, zooplankton, and shellfish. Many of these animals form the foundation of the marine food web. Today, more than a billion people worldwide rely on food from the ocean as their primary source of protein. Ocean acidification puts this important resource at risk. Observations have shown that the northeastern Pacific Ocean, including the Arctic and sub-Arctic seas, is particularly susceptible to significant shifts in pH and calcium carbonate saturation levels. Recent analyses show that large areas of the oceans along the U.S. west coast,, the Bering Sea, and the western Arctic Ocean, will become difficult for calcifying animals within the next 50 years. In particular, animals that form calcium carbonate shells, including corals, crabs, clams, oysters, and tiny free-swimming snails called pteropods, could be particularly vulnerable, especially during the larval stage.,,,

Permafrost temperatures are increasing over Alaska and much of the Arctic. Regions of discontinuous permafrost in interior Alaska (where annual average soil temperatures are already close to 32°F) are highly vulnerable to thaw. Thawing permafrost releases carbon dioxide and methane – heat-trapping gases that contribute to even more warming. Recent estimates suggest that the potential release of carbon from permafrost soils could add as much as 0.4ºF to 0.6ºF of warming by 2100.150 Methane emissions have been detected from Alaskan lakes underlain by permafrost, 151 and measurements suggest potentially even greater releases from thawing methane hydrates in the Arctic continental shelf of the East Siberian Sea.152 However, the response times of Arctic methane hydrates to climate change are quite long relative to methane’s lifetime in the atmosphere (about a decade).153 More generally, the importance of Arctic methane sources relative to other methane sources, such as wetlands in warmer climates, is largely unknown. The potential for a self-reinforcing feedback between permafrost thawing and additional warming contributes additional uncertainty to the high end of the range of future warming. The projections of future climate shown throughout this report do not include the additional increase in temperature associated with this thawing.

Climate Facts

Primary reasons for concern about the Earth's future climate, sea level, and ocean acidification

.

1. CO2 emissions currently match those of the most extreme IPCC emission scenarios
2. The Earth is warming dramatically at a steady rate, and most of the extra heat is going into the oceans
3. Only 2.3% of extra heat is warming the atmosphere, so the recent slowdown in atmospheric temperature increase is just temporary
4. El Nino/La Nina significantly affect atmospheric temperatures, and looking at atmospheric temperature by "event type" shows a steady a steady .16 degree C per decade
5. The complete meltdown of the Arctic could roughly double the rate of warming of the planet as a whole.
6. The IPCC has really underestimated when the summer-time Arctic ocean will likely become ice free
7. The “equilibrium sea level rise” is likely around 10 meters/° C
8. The IPCC is very conservative in is forecasts of sea level rise
9. Flooding at high tide will likely make some coastal cities unusable in the near future
10. The ocean acidification caused by the increased atmospheric CO2 will likely have devastating consequences
11. Carbon from permafrost soils could add as much as 0.4ºF to 0.6ºF of warming by 2100

This Fact Page displays text and images related to global warming and climate change
(Hover your mouse over the text below to "popup" a window with a related text.
Click on the text or image to open a new window with a detailed description.)

 
1.  CO2 emissions currently match those of the most extreme IPCC emission scenarios

If we continue emitting CO2 at the current accelerating rate the result will very likely be a climate that is inhospitable to civilization as we know it
2.  The Earth is warming dramatically at a steady rate, and most of the extra heat is going into the oceans

As a result of the increase in atmospheric CO2, the Earth has been absorbing an excess of about 8 zeta joules of energy/year (the equivalent of a 50 megaton nuclear bomb being exploded every 15 minutes), with almost all of the energy going in to warming the oceans.
3.  Only 2.3% of extra heat is warming the atmosphere, so the recent slowdown in atmospheric temperature increase is just temporary

Only about 2.3% of the excess energy is used to warm the atmosphere, while about 1.3% is used to melt glaciers and about 0.8% is used to melt Arctic sea ice.
4.  El Nino/La Nina significantly affect atmospheric temperatures, and looking at atmospheric temperature by "event type" shows a steady a steady .16 degree C per decade

Snce El Nino and La Nina have such an impact on global atmospheric temperatures, the best way to look at the atmospheric temperature change is to categorize the global temperature by “type of year”, which indicates that the atmospheric temperatures have been increasing at the same steady rate (about .16°C /decade) since 1970
5.  The complete meltdown of the Arctic could roughly double the rate of warming of the planet as a whole.

The loss of the Arctic ice throughout the summer would have a warming effect roughly equivalent to all human activity to date. That is to say, with the ice gone in summer, the planet would have an additional heating effect just as large as the heating effect of all human CO2 and other greenhouse gasses to date.
6.  The IPCC has really underestimated when the summer-time Arctic ocean will likely become ice free

The IPCC has really underestimated when the summer-time Arctic ocean will likely become ice, so it’s temperature estimates are likely low
7.  The “equilibrium sea level rise” is likely around 10 meters/° C

We are already committed to at least 30 feet of sea level rise, enough to force the evacuation of most coastal cities
8.  The IPCC is very conservative in is forecasts of sea level rise

Climate science experts expect that significant sea level rise will occurr much sooner that IPCC does
10.  The ocean acidification caused by the increased atmospheric CO2 will likely have devastating consequences

As a result of the increase in atmospheric CO2, the oceans have become more acidic
11.  Carbon from permafrost soils could add as much as 0.4ºF to 0.6ºF of warming by 2100

Permafrost temperatures are increasing over Alaska and much of the Arctic. Regions of discontinuous permafrost in interior Alaska (where annual average soil temperatures are already close to 32°F) are highly vulnerable to thaw. Thawing permafrost releases carbon dioxide and methane – heat-trapping gases that contribute to even more warming. Recent estimates suggest that the potential release of carbon from permafrost soils could add as much as 0.4ºF to 0.6ºF of warming by 2100.150 Methane emissions have been detected from Alaskan lakes underlain by permafrost, 151 and measurements suggest potentially even greater releases from thawing methane hydrates in the Arctic continental shelf of the East Siberian Sea.152 However, the response times of Arctic methane hydrates to climate change are quite long relative to methane’s lifetime in the atmosphere (about a decade).153 More generally, the importance of Arctic methane sources relative to other methane sources, such as wetlands in warmer climates, is largely unknown. The potential for a self-reinforcing feedback between permafrost thawing and additional warming contributes additional uncertainty to the high end of the range of future warming. The projections of future climate shown throughout this report do not include the additional increase in temperature associated with this thawing.