Showing posts with label polynomial. Show all posts
Showing posts with label polynomial. Show all posts

Saturday, March 18, 2017

Which Trend Is Best?

NASA just released temperature data for February 2017. Should we be worried? Yes, there are many reasons to be very worried.

Let's go back in time. This is from a post written ten years ago:
We may suddenly face a future in which many if not most people will have little or no access to food, water, medicines, electricity and shelter, while diseases go rampant and gangs and warlords loot and devastate the few livable areas left. Human beings as a species will face the risk of total extinction, particularly if many species of animals and plants that humans depend on will disappear. The post continues: Many people are still in denial about the severity of the problem of global warming, the accumulation of dangers and their progression. 

Indeed, even today many people will still deny that such events could strike suddenly, e.g. within a few years time. Many people use linear trends to predict the future many years from now. As an example, the straight blue line on the graph below is a linear trend based on NASA 1880-current meteorological stations data. The problem is that linear trends, especially when based on data that go back many years, can make people overlook important recent changes such as the temperature rise that has taken place over the past few years, the decline of glaciers and sea ice and the recent increases in concentrations of carbon dioxide in the atmosphere.

[ click on image to enlarge ]
An alternative approach is to use recent data, e.g., from the year 2012, and then calculate a polynomial trend that extends a few years into the future. Taking such an approach can result in a polynomial trend (red curved line) that is contained in the NASA Land+Ocean data from January 2012 to February 2017. This trend shows the potential for a 10°C (18°F) rise four years from now, and this should act as a powerful warning.

The appropriateness of linear versus non-linear trends was also discussed earlier at the Controversy page.

In addition to looking at trends that are contained in such data, it makes sense to analyse the different elements contributing to such a rise. Such elements are discussed in more detail at the extinction page, which confirms the potential for a 10°C temperature rise within years, i.e. by the year 2026.

The situation is dire and calls for comprehensive and effective action as described in the Climate Plan.


Links


• Climate Plan
http://arctic-news.blogspot.com/p/climateplan.html

• Ten Dangers of Global Warming
http://arctic-news.blogspot.com/p/ten-dangers-of-global-warming.html

• Extinction
http://arctic-news.blogspot.com/p/extinction.html

• Controversy
http://arctic-news.blogspot.com/p/controversy.html

• Warning of mass extinction of species, including humans, within one decade
http://arctic-news.blogspot.com/2017/02/warning-of-mass-extinction-of-species-including-humans-within-one-decade.html


Tuesday, July 29, 2014

More than 2.5m Sea Level Rise by 2040?

A warming period more than 400,000 years ago pushed the Greenland ice sheet past its stability threshold (which may have been no more than several degrees above pre-industrial temperatures). This resulted in a nearly complete deglaciation of southern Greenland, raising global sea levels some 4.5-6 meters, found a recent study by Reyes et al. Due to melting elsewhere, global mean sea level then was 6 to 13 metres above the present level. Indeed, melting of the entire West Antarctic Ice Sheet can add a further 6-meter rise in sea levels. If the East Antarctic Ice Sheet (EAIS) were to melt as well, sea levels would rise by around 70 metres.

Sea level is now rising by 3.1mm (0.122 inch) per year. Much of this rise is due to rising temperatures, but there are also other factors. One quarter of the rise results from groundwater depletion, while run off from melting ice and glaciers adds another quarter and the remainder is attributed to thermal expansion of sea water. Furthermore, as temperatures rise, feedbacks start to kick in, e.g. the kinetic energy from stronger waves and more intense storms can speed things up.

Clearly, a rapid multi-meter rise would be devastating as it would flood many coastal cities, as well as much of the land now used to grow food. By how much have sea levels been rising recently and how fast can they be expected to rise in the near future?
NASA image, data by the JPL PODAAC, in support of the NASA's MEaSUREs program.
Sea levels have risen by some 60 mm over the past 20 years, as above NASA image shows, which has a linear trendline added. The question is whether a linear trendline is the most appropriate trendline, given that it suggests that a similar rise could be expected over the next 20 years. A polynomial trendline appears to fit the data better, as the animation below shows.


Such a polynomial trendline, however, points at a similar rise (of some 50 mm) in just four years time, with an even more steeper rise to follow, as illustrated by the image below.


And indeed, such a rise doesn't slow down there. A polynomial trendline applied to the data points at a sea level rise of more than 2.5 m (8.2 ft) by the year 2040.



The image below gives an idea of what a sea level rise of six feet (1.829 m) would do to the City of New York. Of course, this is only the sea level rise. Storm surge would come on top of this, as discussed at Ten Dangers of Global Warming.



So, what would be more appropriate, to expect sea levels to continue to rise in a linear way, or to take into account feedbacks that could speed things up? Where such feedbacks could lead to is illustrated by the image below.
[ from: How many deaths could result from failure to act on climate change? click on image to enlarge ]
This calls for comprehensive and effective action, as discussed at the Climate Plan blog.


References

- South Greenland ice-sheet collapse during Marine Isotope Stage 11, Reyes et al. (2014)
http://www.nature.com/nature/journal/v510/n7506/full/nature13456.html

- Nonsustainable groundwater sustaining irrigation: A global assessment, Yoshihide Wada et al. (2012)
http://onlinelibrary.wiley.com/doi/10.1029/2011WR010562/abstract

- Groundwater Depletion Linked to Rising Sea Levels
http://www.waterworld.com/articles/2010/11/groundwater-depletion-linked-to-rising.html

- Assessment of the Jason-2 Extension to the TOPEX/Poseidon, Jason-1 Sea-Surface Height Time Series for Global Mean Sea Level Monitoring, Beckley et al. (2010)
http://www.tandfonline.com/doi/abs/10.1080/01490419.2010.491029

- Feedbacks in the Arctic
http://climateplan.blogspot.com/p/feedbacks.html

- How many deaths could result from failure to act on climate change? (2014)
http://arctic-news.blogspot.com/2014/05/how-many-deaths-could-result-from-failure-to-act-on-climate-change.html



Saturday, April 6, 2013

How much will temperatures rise?

If we take the NASA Annual Mean Land-Ocean Temperatures and draw a projection into the future, temperatures will quickly be 3 degrees Celsius higher than the base period (1951-1980), i.e. well before 2050, as illustrated on image 1. below. 

Image 1. Temperatures will be 3 degrees Celsius higher well before 2050

Above projection appears to be steeper than even the worst-case scenario pictured by the IPCC for years, such as on the image below.

Image 2. from IPCC 2001. Projections of globally averaged surface temperature 2000-2100 are shown for six SRES scenarios and IS92a using a model with average climate sensitivity. The grey region marked "several models all SRES envelope" shows the range of results from the full range of 35 SRES scenarios in addition to those from a range of models with different climate sensitivities. The temperature scale is departure from the 1990 value.
Could temperatures rise faster in future than what the IPCC anticipated in 2001? The answer must be yes! In 2007, the IPCC described that, even if greenhouse gas concentrations in the atmosphere were stabilized for 100 years at year 2000 values (B1), then we would still be committed to a further warming of 0.5°Celsius. This committed warming should not be confused with ‘unavoidable climate change’ over the next half century, which would be greater because forcing cannot be instantly stabilized. And of course, as it turned out, emissions have not been stabilized at 2000 values, but have in fact increased substantially.

As it turned out, the models used by the IPCC made all kinds of assumptions that didn't eventuate. But before deciding to instead settle for a relatively simple extrapolation of observed data, there are some issues that require a further look.  

As discussed in the earlier post Accelerated Arctic Warming, temperatures in the Arctic have been rising at a much faster pace than global temperatures, and if this accelerated rise continues, we can expect a 10 degrees Celsius rise in the Arctic before 2040, as illustrated by image 3. below.  

Image 3. Three kinds of warming - 2: Accelerated warming in the Arctic 
Such a temperature rise in the Arctic will undoubtedly lead to additional greenhouse gas emissions in the Arctic, of carbon dioxide, nitrous oxide and particularly methane, threatening to trigger runaway global warming. 

The image below, from the methane-hydrates blog, combines these three kinds of warming, showing global temperatures that soon catch up with accelerated Arctic warming, as heatwaves at high latitudes will cause wildfires, in particular in Siberia, where firestorms in peat-lands, tundras and forests could release huge amounts of emissions, including soot, much of which could settle on the Himalayan plateau, darkening the ice and snow and resulting in more local heat absorption. Rapid melt of glaciers will then cause flooding at first, followed by dramatic decreases in the flow of river water that up to a billion people now depend on for water supply and irrigation.

In other words, the situation looks much more dire than what most models make us believe; the more reason to adopt the climate plan that is also described at the post at the methane-hydrates blog.

Image 4. Three kinds of warming - 1, 2 and 3 


References

- IPCC (TAR) - Climate Change 2001: Synthesis Report

- IPCC (AR4) - Climate Change 2007: Working Group I: The Physical Science Basis

- Accelerated Arctic Warming

- Methane hydrates