2 degrees Celsius - what that means.


In 2015 we were told Earth had passed the 1C temperature rise since industrial age levels. During talks leading up to Paris COP-21 debate centered around limiting temperature rise to 1.5C. To understand the background to these self-imposed limits and how they're calculated requires urgent attention as the planet is now warming at ever increasing rates.

The global climate change deal agreed in Paris in December 2015 pledged to “hold the increase in the global average temperature to well below 2C above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5C.” Vulnerable countries, such as low-lying islands, have warned that 2C of climate change would wipe their nations from the map. Understanding the different impacts from 1.5C or 2C of warming has been made more urgent by the recent run of record temperatures, with 2014 and 2015 breaking long-term records. In February, the global temperature was 1.34C above the average from 1951 – 1980 according to Nasa data. link

Global warming passes 1C in 2015 – UK Met Office - link
Global warming halfway to UN’s 2C limit – New Scientist: link

Latest news:

May 4 2017:  When oil companies strategy is 4C rise. In 2014, Shell was accused of pursuing a business strategy on 4C warming. Now oil and gas company Santos has admitted its business plans are based on a climate change scenario of a 4C rise in global temperatures, at odds with internationally agreed efforts. Will Steffen (Australian National University) said the difference between the ice age and the Holocene age, which Earth has been in for about 12,000 years, was 4C. “You’d be locking in tens of metres of sea-level rise, and you can forget about the world cities.” There have already been warnings from UN agencies that current government pledges only hold warming to 3C - well beyond what climate scientists consider the limit of safety. link     


  • Evidence on the 1.5C threshold
  • Warnings
  • Is there a need for a target?
Evidence on the 1.5C threshold

April 2017: Analysis: Just four years left of the 1.5C carbon budget. Four years of current emissions would be enough to blow what’s left of the carbon budget for a good chance of keeping global temperature rise to 1.5C. link   

January 2017: Planet could breach 1.5C rise one year from now.  As of now, by the least optimistic calculations, the world has one year to stop pumping CO2 into the atmosphere if we want to stop climate change at 1.5 degrees Celsius of warming, the aim of the Paris climate agreement. A carbon countdown clock from researchers at the Mercator Research Institute on Global Commons and Climate Change does the math, estimating the time left at current emission levels. Even with a higher limit of two degrees of warming and the most optimistic projections, we still only have about 23 years to fully transition to a carbon-free economy.  link

August 2016: Scientists warn world will miss key climate target.  Leading climate scientists have warned that the Earth is perilously close to breaking through a 1.5C upper limit for global warming, only eight months after the target was set. link   (Temperatures peaked at 1.38C above pre-industrial levels in February and March 2016 – link

June 2016: What would a global warming increase of 1.5 be like? Scientists are only now getting out of the blocks to address what a 1.5C world would look like, because until recently it sounded like a political and technological impossibility. So what is at stake? There are two issues to address. First, what would be gained by going the extra mile for 1.5? And second, what would it take to deliver? It looks like 1.5C matters a great deal. So how hard would it be to keep warming to that level? After all, last year was one degree above pre-industrial levels. And at various times in the past six months, global average temperatures have sometimes gone above 1.5C.  link

May 2016: World CO2 concentration teetering on point of no return. The world is hurtling towards an era when global concentrations of carbon dioxide never again dip below the 400 parts per million milestone, as two important measuring stations sit on the point of no return. The global average, after controlling for the seasonal cycle, popped above 400ppm late 2015. Within a couple of years, the seasonal dips will never drop below 400ppm in the global average. link

April 2016: New study shows why half a degree matters.  European researchers have found substantially different climate change impacts for a global warming of 1.5C and 2C by 2100, the two temperature limits included in the Paris climate agreement. The additional 0.5C would mean a 10-cm-higher global sea-level rise by 2100, longer heat waves, and would result in virtually all tropical coral reefs being at risk. The research is published (21 April) in Earth System Dynamics, an open access journal of the European Geosciences Union, and is presented at the EGU General Assembly. link

April 2016: Flirting with the 1.5C threshold.  A Climate Central analysis shows that the world will have to dramatically accelerate emissions reductions if it wants to meet a 1.5C goal. February exceeded the 1.5C target at 1.55C, marking the first time the global average temperature has surpassed the sobering milestone in any month. March followed suit checking in at 1.5C. January’s mark of 1.4C, put the global average temperature change from early industrial levels for the first three months of 2016 at 1.48C. link

December 2015: The 2C target is a value judgment: Greenland’s ice sheet could disintegrate in a 2C world. As the climate negotiations in Paris proceed, the ultimate goal is to ensure that warming stays “well below” 2 degrees Celsius above pre-industrial levels, according to one option in a recent draft agreement text, and many countries want to hold it even lower than that. The current pledges, the UN has said repeatedly, are not strong enough to ensure that goal. So the pledges simply have to get tougher. However, there’s a problem. In two separate new studies just out scientists challenge the 2C target, originally proposed back in the 1990s. The authors list many very severe impacts of climate change that could be expected at 2 C or even below it. link

April 2016: Study reveals greater climate impacts of 2C rise. A difference of half a degree centigrade may be barely noticeable day to day, but the difference between 1.5C and 2C of global warming is a shift into a new, more dangerous climate regime, according to the first comprehensive analysis of the issue. Scientists found the additional 0.5C would lead to longer heatwaves, greater droughts and, in the tropics, reduced crop yield and all coral reefs being put in grave danger. link

Weekly CO2 readings from Mauna Loa, Hawaii.  link


January 2017: Global 2C warming limit not feasible, warns top economist. The respected Yale climate economist William Nordhaus, dismisses the Paris climate deal as “rhetoric”. The academic ran the numbers through his economic model known as DICE and came up with some bleak answers. “The international target for climate change with a limit of 2C appears to be infeasible with reasonably accessible technologies – and this is the case even with very stringent and unrealistically ambitious abatement strategies,” he writes. “This is so because of the inertia of the climate system, of rapid projected economic growth in the near term, and of revisions in several elements of the model. A target of 2.5C is technically feasible but would require extreme policy measures.” link

June 2016: Window for avoiding 1.5C global warming ‘closed’. Scientists have bad news for people on the front lines of climate change. The 1.5C global warming limit vulnerable countries fought hard to include in the Paris Agreement may already be out of reach. “The window for limiting warming to below 1.5C with high probability and without temporarily exceeding that level already seems to have closed,” the report found. link

September 2009: 4C rise now unavoidable: In a dramatic acceleration of forecasts for global warming, UK scientists say the global average temperature could rise by 4C (7.2F) as early as 2060.  link

Is there a need for a target?

Should we halt CO2 emissions altogether? If CO2 emissions came to a sudden halt, the carbon dioxide already in Earth's atmosphere could continue to warm our planet for hundreds of years, according to a Princeton University-led study. The study suggested it might take a lot less carbon than previously thought to reach the global temperature scientists deem unsafe. The researchers simulated an Earth on which, after 1,800 billion tons of carbon entered the atmosphere, all CO2 emissions suddenly stopped. Scientists commonly use the scenario of emissions screeching to a stop to gauge the heat-trapping staying power of CO2. Within a millennium of this simulated shutoff, the carbon itself faded steadily with 40% absorbed by Earth's oceans and landmasses within 20 years and 80% soaked up at the end of the 1,000 years. By itself, such a decrease of atmospheric CO2 should lead to cooling. But the heat trapped by the CO2 took a divergent track. After a century of cooling, the planet warmed by 0.37 degrees Celsius (0.66 Fahrenheit) during the next 400 years as the ocean absorbed less and less heat. While the resulting temperature spike seems slight, a little heat goes a long way here. Earth has warmed by only 0.85 degrees Celsius (1.5 degrees Fahrenheit) since pre-industrial times. The Intergovernmental Panel on Climate Change estimates that global temperatures a mere 2 degrees Celsius (3.6 degrees Fahrenheit) higher than pre-industrial levels would dangerously interfere with the climate system. To avoid that point would mean humans have to keep cumulative CO2 emissions below 1,000 billion tons of carbon, about half of which has already been put into the atmosphere since the dawn of industry. link

January 2017: What’s so special about 2C? The simple answer is that it is a target that could be politically agreed on the international stage. It was first suggested in 1975 as an upper threshold beyond which we would arrive at a climate unrecognisable to humans. Temperature increases beyond 1C may elicit rapid, unpredictable and non-linear responses that could lead to extensive ecosystem damage. When the planet was 2C colder than during the industrial revolution, we were in the grip of an ice age  link

October 2014: Ditch the 2C warming goal. The 2C target has been repeated like a mantra, mentioned thousands of times in newspaper articles. But two academics in the prestigious journal Nature, argue that the 2C target has outlived its usefulness. They say it should be abandoned and replaced with a series of measures, “vital signs”, of the planet’s health. Under the headline, “Ditch the 2C warming goal”, they argue the 2C limit is “politically and scientifically ... wrong-headed”, it is “effectively unachievable” and it has let politicians off the hook, allowing them to “pretend that they are organising for action when, in fact, most have done little.” But as new numbers show global CO2 emissions at record levels and on an ever-upward trend hat puts the world on course for temperatures well above 2C, researches Victor and Kennel argue 2C is effectively unachievable. link  

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