Timeline: How The World Discovered Global Warming
2. december 2011
Her til morgen var der via Reuters’ miljønyhedsservice Planet Ark World Environment News et telegram med en tidslinje, How The World Discovered Global Warming,¹ som giver et fint overblik over udviklingen i forståelsen af den globale opvarmning og det forhold, at det for en stor dels vedkommende er et menneskeskabt problem. Så jeg har tilladt mig at kopiere den ind nedenfor.
Det kunne have været interessant, hvis tidslinjen også havde medtaget udviklingen i forståelsen af hvilken indsats, der er nødvendig for at afbøde problemerne. Det er blot få år siden, at man talte om 550 ppm som den maksimale koncentration af CO2 – ikke fordi man havde nogen klar forståelse af, at det globale klima ville holde sig nognelunde stabilt, hvis man holdt koncentrationen under 550 ppm, men fordi videnskabsmændene teoretisk havde diskuteret spørgsmålet, hvad en fordobling af CO2-niveauet i forhold til det førindustrielle niveau (på omkring 280 ppm) ville betyde i global opvarmning. Først omkring 2007-08 bliver det mere klart, at 550 ppm sandsynligvis vil medføre en global temperaturstigning på omkring 6ºC, og at dette vil kunne udløse såkaldte Tipping Points, hvorfra klimaforandringerne bliver selvaccelererende. Målsætningen blev derfor strammet til 450 ppm.
Men selv denne grænse er problematisk. Den modsvarer en 50% chance for, at temperaturstigningen ikke når over 2ºC – hvilket på ingen måde er betryggende. På længere sigt vil en koncentration på 450 ppm sandsynligvis medføre fuld afsmeltning af alle klodens ismassiver og en deraf følgende havstigning på 70-75 meter. I 2008 fastslog NASAs klimaforskningsafdeling således, at vi for at langtidsstabilisere det globale klima må tilbage under 350 ppm.
Ved klimatopmødet i København i 2009 var der da også meget stærke kræfter for at få 350 ppm og max. 1½° C indført som overordnet målsætning. Det endte ved 450 ppm og 2ºC. Men et flertal af verdens lande (117 af 194) pressede på til det sidste på for at få en målsætning på 350 ppm / 1½ºC indføjet i Copenhagen Accord. Og der er er tilsvarende i disse dage i Durban et markant pres på at få verden til at stå sammen om en målsætning på 350 ppm / 1½ºC, ikke mindst fra de fattigste lande, hvor klimaforandringerne i dag gennemgående er mest fremskredne.
Inden for ganske få år er klimaudfordringen vokset voldsomt: Ikke bare er det nødvendigt på globalt plan at iværksætte en målrettet omstillingsproces både i de gamle I-lande og de voksende udviklingslande, som i den nuværende situation har overtaget en stor del af den CO2-tunge fremstillingsvirksomhed. Hvis målsætningen er 350 ppm og niveauet i dag allerede er på 390 ppm, så er det ikke nok at reducere udledningerne. Vi må yderligere finde måder, hvorpå vi kan trække CO2 ud af atmosfæren.
Derfor er det vitalt, at der kommer et resultat ud af forhandlingerne i Durban. For blot få uger siden gjorde IEA det klart, at det var ved at være sidste chance, hvis vi skulle nå at standse udviklingen inden 450 ppm / 2ºC. På den baggrund er en række af de store landes nølen helt utilstedelig.
Se tidligere blog-indlæg: IEA: Fem år til at vende udviklingen, NASA-forskere varsler havstigninger på op til 75 meter, James Hansen: Sidste udkald, Gambling med vores fælles fremtid, Klima-scenario med blot 1º temperaturstigning, Rajendra Pachauri støtter op om en målsætning på 350 ppm, Hvor store CO2-reduktioner skal der til? og Visualisering af CO2-udviklingen.
På hjemmesiden global-opvarmning.com har klimadebat.dks redaktør Jeppe Branner lavet en rigtig god dansksproget historisk redegørelse for udviklingen i vores forståelse af klimaudfordringen.²
Alister Doyle, David Fogarty & David Cutler: Timeline: How The World Discovered Global Warming, (Reuters) Planet Ark 02.12.2011.¹
Jeppe Branner: Global opvarmning. En forunderlig rejse tilbage i tiden, global-opvarmning.com januar 2012.²
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Timeline
Following is a look at how the world discovered global warming and international steps to try to address it:
300 BC – Theophrastus, a student of Greek philosopher Aristotle, documents that human activity can affect climate. He observes that drainage of marshes cools an area around Thessaly and that clearing of forests near Philippi warms the climate.
17th century – Flemish scientist Jan Baptista van Helmont discovers that carbon dioxide is given off by burning charcoal.
18th century – The Industrial Revolution starts, bringing rising use of fossil fuels.
1820s – French mathematician Jean-Baptiste Joseph Fourier suggests something in the atmosphere is keeping the world warmer than it would otherwise be, a hint at the greenhouse effect.
1830s – Swiss naturalist Louis Agassiz presents evidence of past changes in Alpine glaciers, pointing to ancient Ice Ages and showing that the climate has not always been stable.
1860s – Irish scientist John Tyndall shows that molecules of gases such as water vapour and carbon dioxide trap heat. He wrote that changes “could have produced all the mutations of climate which the researches of geologists reveal.”
1896 – Swedish chemist Svante Arrhenius becomes the first to quantify carbon dioxide’s role in keeping the planet warm. He later concluded that burning of coal could cause a “noticeable increase” in carbon levels over centuries.
1950s – U.S. scientist Charles Keeling sets up stations to measure carbon dioxide concentrations in the atmosphere at the South Pole and at Mauna Loa, Hawaii. The measurements have shown a steady rise.
1965 – U.S. President Lyndon Johnson tells Congress: “This generation has altered the composition of the atmosphere on a global scale through … a steady increase in carbon dioxide from the burning of fossil fuels.”
1988 – British Prime Minister Margaret Thatcher tells the United Nations: “The problem of global climate change is one that affects us all and action will only be effective if it is taken at the international level. It is no good squabbling over who is responsible or who should pay.”
1988 – The United Nations sets up the Intergovernmental Panel on Climate Change (IPCC) to assess the scientific evidence.
1992 – World leaders agree the U.N. Framework Convention on Climate Change, which sets a non-binding goal of stabilising greenhouse gas emissions by 2000 at 1990 levels, a target not met overall.
1995 – The IPCC concludes for the first time that humans are causing global warming, saying: “The balance of evidence suggests a discernible human influence on global climate.”
1997 – The Kyoto Protocol is agreed in Japan; developed nations agree to cut their greenhouse gas emissions on average by at least 5 percent below 1990 levels by 2008-12. The United States stays out of the deal.
2001 – The IPCC concludes it is “likely,” or at least 66 percent probable, that human activities are the main cause of recent warming.
2001 – President George W. Bush notes the U.S. National Academy of Sciences says greenhouse gases are rising “in large part due to human activity.” He adds: “Yet, the Academy’s report tells us that we do not know how much effect natural fluctuations in climate may have had on warming. We do not know how much our climate could, or will change in the future.”
2007 – The IPCC says it is “very likely,” at least 90 percent certain, that humans are to blame for most of the observed warming trend of the past 50 years. It also said warming of the planet was “unequivocal.”
2009 – A conference of 193 countries agree in December to “take note” of a new Copenhagen Accord to fight climate change, after U.N. talks in Denmark. The accord is not legally binding and does not commit countries to agree a binding successor to the Kyoto Protocol when its first stage ends in 2012. The conference did recognize “the scientific view that the increase in global temperature should be below 2 degrees Celsius” and “deep cuts in global emissions are required.”
2010 – A deal among 190 nations to slow climate change throws a lifeline to U.N.-led talks.
2011 – More than 190 nations meet in Durban, South Africa, to try to agree what to do after the first stage of the Kyoto Protocol expires in 2012 and on a Green Climate Fund to channel billions of dollars to poorer nations to green their economies and help them protect against the effects of climate change.
