2 degrees Celsius - what that means


The Paris agreement text commits the world’s governments to limiting global warming to no more than 2C above preindustrial levels. But the emissions reductions it lays out don’t actually get us there. Even if all the world’s countries meet their targets (which is very unlikely, since the targets are non-binding) we’ll still be hurtling toward more than 3C of global warming, and possibly as high as 4.4C by 2100. What might our planet look like if it warms by 4C? No one can say for certain, but projections show that this level of warming is likely to bring about heatwaves not seen on Earth for 5 million years. Southern Europe could dry up into a desert. Sea levels could rise by 1.2 meters before the century is out, drowning cities like Amsterdam and New York. Furthermore, 40% of species will be at risk of extinction. Most of our rainforests will wither away. Crop yields could collapse by 35%, destabilising the world’s food system and triggering widespread famine. In short, a 4C world looks very bleak indeed. link

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


Latest news:

April 26 2018: Bold action needed before 2020 to hold global warming below 1.5C. A recent report found that unless bold climate action is taken in the next couple of years, before 2020, it may become impossible to hold global warming below 1.5C. As important as it is to measure global progress toward cutting greenhouse gas emissions, it must be recognised that the national contributions under the Paris Agreement don’t legally commence until 2020. 
Since the beginning of the UN climate change negotiations and through the Paris Agreement, it has always been understood that developed countries would take the lead in transitioning to low-carbon energy sources because they are responsible for the vast majority of historic emissions. Many developed countries’ pre-2020 obligations remain unmet and now some seem eager to forego early action altogether. link



  • Origins of the 2C limit
  • Evidence on the 1.5C threshold
  • Warnings of increasing temperatures
  • Is there a need for a target?
 Origins of the 2C limit

Origins of the 2C limit. In 2010, when the 2C goal was adopted at a major conference in Cancun, Mexico, the carbon budget for 450 ppm, or 2C, was formidably tight: Only a third was left, 1,000 gigatons of CO2. Since humans were emitting 40 gigatons a year, the carbon budget would be easily blown before midcentury. The 2C goal is a theoretical limit for how much warming humans could accept. For leading climatologist James Hansen, even the 2C limit is unsafe. And without emissions cuts, global temperatures are projected to rise by 4C by the end of the century. Temperatures have already risen 1.2 to 1.3C .  According to the Mercatur Research Institute, the 1.5C budget is more or less blown—a widely shared conclusion. Without a drastic increase in international action on cutting emissions, they say, the carbon budget for 2C will likely be blown by 2030. (You can check the Institute’s running carbon budget clock here.)  link to December 2017 article – ‘The dirty secret of the world’s plan to avert climate disaster.)

Evidence of 1.5 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

In February 2016, the global temperature was 1.34C above the average from 1951 – 1980 according to Nasa data. 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

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.  link

Weekly CO2 readings from Mauna Loa, Hawaii.  link

Warnings of increasing temperatures

February 2018: Technology to stay below 2C isn’t promising. In the two-degrees emissions scenarios, techniques (including CCS, reforestation) have to start soaking up at least 11 billion tons of CO2 per year around 2050 in order to offset our continued emissions. If we bank on that future offset, but it fails to materialize, we will find that it’s too late to cut our emissions and limit global warming to two degrees Celsius. A report by EASAC (European Academies Science Advisory Council) finds that few options look like they could scale up to 3 or 4 billion tons, and none is on track to do so at this point. link

January 2018: Met Office warns of global temperature rise exceeding 1.5C limit. Global temperatures have been steadily rising over the past 20 years, and in each of the last three years averages have topped the 1C threshold. Global temperatures could break through the internationally agreed upper 1.5C limit within the next five years, according to a forecast by British scientists. link

November 2017: As for 1.5 degrees? Forget itAs negotiators in Bonn begin assembling a rule book for ensuring that national pledges made in Paris are fulfilled, there comes a hard dose of reality. Those pledges, which constrain greenhouse gas emissions from now to 2030, will only deliver a third of the cuts needed to put the world on track to keep warming below the promised 2C. link

October 2017: UN - Prepare for a world 3C warmer in 80 years. As things stand, the UN says, even fully implementing the goals of the Paris Agreement will deliver only one third of what is needed for the world to avoid the worst impacts of climate change. The United Nations assessment says a temperature increase of at least 3C by 2100 is very likely. Also, action by the private sector and by cities and other groups below national level is not increasing fast enough to help to close the gap. link

May 2017: What the world will look like 4C warmer.  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’. 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

May 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   

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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