Climate change :wat we can do?

 

The current warming trend is of particular significance because most of it is very likely human-induced and proceeding at a rate that is unprecedented in the past 1,300 years.
Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. This body of data, collected over many years, reveals the signals of a changing climate.
The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century.² Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many instruments flown by NASA. There is no question that increased levels of greenhouse gases must cause the Earth to warm in response.
Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that the Earth’s climate responds to changes in greenhouse gas levels. They also show that in the past, large changes in climate have happened very quickly, geologically-speaking: in tens of years, not in millions or even thousands.

Sea level rise

 

 

Their reassessment of tide gauge data from 1900-1990 found that the world's seas went up more slowly than earlier estimates - by about 1.2mm per year.
But this makes the 3mm per year tracked by satellites since 1990 a much bigger trend change as a consequence.
It could mean some projections for future rises having to be revisited.
"Our estimates from 1993 to 2010 agree with [the prior] estimates from modern tide gauges and satellite altimetry, within the bounds of uncertainty. But that means that the acceleration into the last two decades is far worse than previously thought," said Dr Carling Hay from Harvard University in Cambridge, Massachusetts.
"This new acceleration is about 25% higher than previous estimates," she told BBC News.
Dr Hay and colleagues report their re-analysis in this week's edition of the journal Nature.

Scientists have calculated the various contributions to sea-level rise, such as melting land ice

Tide gauges have been in operation in some places for hundreds of years, but pulling their data into a coherent narrative of worldwide sea-level change is fiendishly difficult.Historically, their deployment has been sparse, predominantly at mid-latitudes in the Northern Hemisphere, and only at coastal sites. In other words, the instrument record is extremely patchy.
What is more, the data needs careful handling because it hides all kinds of "contamination".
Scientists must account for effects that mask the true signal - such as tectonic movements that might force the local land upwards - and those that exaggerate it - such as groundwater extraction, which will make the land dip.
Attention needs to be paid also to natural oscillations in ocean behaviour, which can make waters rise and fall on decadal timescales.
Previous efforts to untangle the record concluded that sea levels rose through much of the last century by around 1.6-1.9mm per year.
These figures were included in the most recent Intergovernmental Panel on Climate Change (IPCC) report on the state of the planet.
But these numbers have been somewhat problematic because they are at odds with the calculated contributions to global ocean rise - namely, the volumes of water coming from melting land ice, the expansion of the seas from global warming, and changes in the amount of global water held on the continents. Simply put, the calculated contributions were about 0.5mm per year short of what previous tide-gauge assessments were suggesting they should be.
Dr Hay's and colleagues' study makes another attempt to sort through the instrument record, and they find the 1900-1990 rises to have been overstated.
Their rate for this period is 1.2mm per year, which neatly closes the contributions "budget gap".
Dr Hay said: "What we have done, which is a bit different from past studies, is use physical models and statistical models to try to look for underlying patterns in the messy tide gauge data observations.
"Each of the different contributions actually produces a unique pattern, or fingerprint, of sea-level change. And what we try to do is model these underlying patterns and then use our statistical approach to look for the patterns in the tide gauge observations. That allows us to infer global information from the very limited records."

The modern tide gauge is now a highly sophisticated tool. Coastal instruments have recorded sea level change at some locations for more than 200 years

In the last IPCC report, global mean sea-level rise for 2081−2100 was projected to be between 26cm (at the low end) and 82cm (at the high end), depending on the greenhouse emissions path this century. If the Hay analysis is reproduced by peer groups, it may prompt the scientific community to revisit these future sea-level projections and some of the other estimates that envisage even larger changes in the decades ahead.
Commenting, Dr Paolo Cipollini at the UK's National Oceanography Centre, said the Nature study was an important new contribution to the field.
Having a good view of historical change, he explained, would allow researchers to test their models of the processes driving sea-level rise by permitting them to do "hindcasts" - to check whether those models could reproduce the past before making confident projections of the future.
"But let's not lose sight of the central message that at the moment we have a very strong consensus on the 3.2mm per year of sea-level rise coming from satellites and modern tide gauges, and that any future projection should be based mainly on our understanding of the processes of sea-level rise, which really we need quantify better for later IPCC reports."
The "gold standard" satellite record of sea-level rise is maintained by the Jason series of spacecraft, which have an unbroken record of measurements stretching back to 1992.
Jason-3, the latest incarnation, launches this year, along with the EU's Sentinel-3 spacecraft,

which has been tasked with starting another continuous - and independent - sequence of observations.

Global temperature rise

Scientists have high confidence that global temperatures will continue to rise for decades to come, largely due to greenhouse gasses produced by human activities. The Intergovernmental Panel on Climate Change (IPCC), which includes more than 1,300 scientists from the United States and other countries, forecasts a temperature rise of 2.5 to 10 degrees Fahrenheit over the next century.
According to the IPCC, the extent of climate change effects on individual regions will vary over time and with the ability of different societal and environmental systems to mitigate or adapt to change.
The IPCC predicts that increases in global mean temperature of less than 1.8 to 5.4 degrees Fahrenheit (1 to 3 degrees Celsius) above 1990 levels will produce beneficial impacts in some regions and harmful ones in others. Net annual costs will increase over time as global temperatures increase.
"Taken as a whole," the IPCC states, "the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time." 1
Below are some of the impacts that are currently visible throughout the U.S. and will continue to affect these regions, according to the Third National Climate Assessment Report 2, released by the U.S. Global Change Research Program:
Northeast. Heat waves, heavy downpours, and sea level rise pose growing challenges to many aspects of life in the Northeast. Infrastructure, agriculture, fisheries, and ecosystems will be increasingly compromised. Many states and cities are beginning to incorporate climate change into their planning.
Northwest. Changes in the timing of streamflow reduce water supplies for competing demands. Sea level rise, erosion, inundation, risks to infrastructure, and increasing ocean acidity pose major threats. Increasing wildfire, insect outbreaks, and tree diseases are causing widespread tree die-off.
Southeast. Sea level rise poses widespread and continuing threats to the region’s economy and environment. Extreme heat will affect health, energy, agriculture, and more. Decreased water availability will have economic and environmental impacts.
Midwest. Extreme heat, heavy downpours, and flooding will affect infrastructure, health, agriculture, forestry, transportation, air and water quality, and more. Climate change will also exacerbate a range of risks to the Great Lakes.
Southwest. Increased heat, drought, and insect outbreaks, all linked to climate change, have increased wildfires. Declining water supplies, reduced agricultural yields, health impacts in cities due to heat, and flooding and erosion in coastal areas are additional concerns.

Warming oceans

 

Ocean heat content data to a depth of 2,000 meters, from NOAA.

Wow, was this a bad year for those who deny the reality and the significance of human-induced climate change. Of course, there were the recent flurry of reports that 2014 surface temperatures had hit their hottest values ever recorded. The 2014 record was first called on this blog in December and the final results were reported as well, here. All of this happened in a year that the denialists told us would not be very hot.
But those denialists are having a tough time now as they look around the planet for ANY evidence that climate change is not happening. The problem is, they’ve been striking out.
And just recently, perhaps the most important bit of information came out about 2014 – how much the Earth actually warmed. What we find is that the warming is so great, NOAA literally has to remake its graphs. Let me explain this a bit.
We tend to focus on the global temperature average which is the average of air temperatures near the ground (or at the sea surface). This past year, global air temperatures were record-breaking. But that isn’t the same as global warming. Global warming is properly viewed as the amount of heat contained within the Earth’s energy system. So, air temperatures may go up and down on any given year as energy moves to or from the air (primarily from the ocean). What we really want to know is, did the Earth’s energy go up or down?

So what do the new data show? Well, it turns out that the energy stored within the ocean (which is 90% or more of the total “global warming” heat), increased significantly. A plot from NOAA is shown above. You can see that the last data point (the red curve), is, literally off the chart.

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The folks at NOAA do a great job updating this graph every three months or so. We can now say that the 2014 Earth had more heat (thermal energy) than any year ever recorded by humans. We can also say that the folks at NOAA will likely have to rescale their graph to capture the new numbers. The NOAA site is updated by Dr. Tim Boyer and can be found here. Click on slide 2 to view the relevant image.
If people want to read a review of ocean heating that is written for a general audience, I suggest our recent peer-reviewed paper which can be found here.
So when we look back on 2014 and the records that fell, it gives us some pause about the so-called pause (hat-tip to Dr. Greg Laden for that phrase). Some people tried to tell us global warming had “paused”, that it ended in 1998, or that the past 15 years or so had not seen a change in the energy of the Earth. This ocean warming data is the clearest nail in that coffin. 

Flowing meltwater from the Greenland ice sheet

Shrinking ice sheets

This section is all about ice shelves. Ice shelves are floating ice, connected to the mainland. They receive ice from glaciers flowing into them from the mainland, from accumulation from snow directly onto the ice shelf, and from sea water freezing onto the bottom of the ice shelf. Most mass loss from the Antarctic continent is from ice shelves, and most of this is from just a few small ice shelves around the Antarctic Peninsula and West Antarctica.
Ice shelves can collapse dramatically. This can occur over just a few weeks, following progressive thinning by warm ocean waters below, and from excessive melting during a warm summer above. If an ice shelf collapses, it changes the boundary conditions for the glaciers that flow into the ice shelf. This means that ice-shelf tributary glaciers accelerate, thin and recede following ice-shelf collapse. So, although ice shelves are already floating and therefore do not contribute to sea level rise when they collapse, ice-shelf removal has significant consequences for the grounded glaciers on the mainland.
More information:

Ice shelves

Landsat Image Mosaic of Antarctica (LIMA) showing location of key ice shelves.

An ice shelf is a floating extension of land ice. The Antarctic continent is surrounded by ice shelves. They cover >1.561 million km² (an area the size of Greenland)[1], fringing 75% of Antarctica’s coastline, covering 11% of its total area and receiving 20% of its snow.
The difference between sea ice and ice shelves is that sea ice is free-floating; the sea freezes and unfreezes each year, whereas ice shelves are firmly attached to the land. Sea ice contains icebergs, thin sea ice and thicker multi-year sea ice (frozen sea water that has survived several summer melt seasons, getting thicker as more ice is added each winter).
In the photographs below, you can see the flat, floating ice shelf is almost featureless. The ice flows from the mainland into the sea, and when it becomes deep enough it floats.

Ice shelf flow

Simplified cartoon of a tributary glacier feeding into an ice shelf, showing the grounding line (where the glacier begins to float).

Ice shelves receive ice in several ways: flow of ice from the continent, surface accumulation (snow fall) and the freezing of marine ice to their undersides. Ice shelves lose ice by melting from below (from relatively warm ocean currents), melting above (from warm air temperatures) and from calving icebergs.  This is a normal part of their ablation.
Ice shelves can be up to 2000 m thick, with a cliff edge that’s up to 100 m high. They often show flow structures on their surface – a relic of structures formed on land.

Sea ice

This image of Antarctic sea ice is from the NASA Scientific Visualisation Studio, showing the Earth on September 21st 2005. Source: Wikimedia Commons.

Sea ice surrounds the polar regions. On average, sea ice covers up to 25 million km², an area 2.5 times the size of Canada. Sea ice is frozen ocean water. The sea freezes each winter around Antarctica.
Sea ice can modify climate change’s impact on terrestrial ice because it is highly reflective and because it has a strongly insulating nature. Each year, the extent of sea ice varies according to climate variability and long-term climate change.

Breaking ice in Fridtjov Sound

The first year sea ice fractures under the ship

Red paint on the sea ice from ice breaking

Frozen first year sea ice around Rothera

In the Arctic, sea ice extent is steadily decreasing, with a trend of -5.3±00.6% per decade since 1985[10], as a result of long-term climate change. Year-on-year variations reflect normal variability. Because removal of sea ice changes the reflectivity of the Arctic, a diminishing sea-ice extent amplifies warming.

Frozen winter sea ice trapping calved icebergs from the margin of a tidewater glacier

Sea ice in the Antarctic is currently increasing. This is associated with cooling sea surface temperatures in the Southern Ocean, in particular near the Ross Ice Shelf. Causes of this increasing Antarctic sea ice, which are contrasted with shrinking glaciers and ice shelves and warming deeper ocean current temperatures and atmospheric air temperatures, include changes to the Southern Annual Mode due to intensification and migration of the predominant Southern Ocean Westerlies, and cooler sea surface temperatures as a result of increased glacier and ice-shelf melting