What did the latest IPCC report on climate change actually say?

Climate protesters in Washington D.C., 2017. Image: Getty.

The world’s climate scientists have spoken: if we want to limit human-induced global warming to 1.5℃ we probably can. But it will be tough, given where we’re starting from.

That’s the conclusion of a new report by the UN’s Intergovernmental Panel on Climate Change (IPCC). The focus on 1.5℃ is the result of years of international negotiation. Starting in 1994, a central aim of the UN’s climate change efforts (the Framework Convention on Climate Change, or UNFCCC) was to stabilise greenhouse gas concentrations at a level that would “prevent dangerous anthropogenic interference with the climate system”. Much was written on what this meant, particularly the word “dangerous”.

Negative impacts of climate change occur on a continuum, and defining a point at which climate change becomes dangerous is difficult and contentious. On the other hand, climate change negotiations are difficult without some target to work towards.

Fifteen years later, the UNFCCC’s Copenhagen Accord introduced a 2℃ target, and its 2015 Paris Agreement was even more specific: it “aims to strengthen the global response to the threat of climate change... by holding the increase in... temperature to well below 2℃ above pre-industrial levels and pursuing efforts to limit the... increase to 1.5℃”.

The IPCC provides scientific advice to the UNFCCC, which makes policy, and the IPCC itself has never stated a temperature target. It does however list climate change risks using five “reasons for concern”. These include impacts such as “unique and threatened ecosystems and cultures” (such as coral reefs) and “extreme weather events”, each of which is rated on a scale from “undetectable” to “very high”. The IPCC’s most recent (2014) Fifth Assessment of the scientific evidence found that at around 1.5℃ warming there was a transition from moderate to high risk for threatened ecosystems and cultures and for extreme weather events. Thus there is consistency between the Paris and IPCC assessments.

The Paris Agreement asked the IPCC to report on the impacts of global warming of 1.5℃, and this new publication is the result. Its tone is not “we must avoid 1.5℃ warming”, as you might think from many commentators, but more “if we want to avoid 1.5℃ warming, this is what must be done”. The report contrasts the impact of 1.5℃ and 2℃ warmings, giving information on what would be gained by the extra effort needed to limit warming to 1.5℃.

As the IPCC’s reports are largely based on a critical assessment and synthesis of published scientific papers, many of its latest conclusions are unsurprising. There are many well recognised uncertainties in understanding climate change - for instance, even if we set a course aiming to hit 1.5℃ (which is mostly determined by future CO₂ emissions), we could end up hitting, say, 1℃ or 2℃ instead. The report provides uncertainty ranges in its estimates and confidence levels, based on expert judgement.


The new report tells us that human activity has already caused about 1℃ of global warming, while at the present rate of warming (0.2℃ per decade) we’ll hit 1.5℃ by about 2040. National pledges made as part of the Paris Agreement still mean we are on course for warming of about 3℃ by 2100, meaning four of the five “reasons for concern” would then be in the high to very-high risk category.

Achieving the 1.5℃ target will require anthropogenic CO₂ emissions to decline by 45 per cent by 2030 (relative to 2010). By 2050, they will need to reach “net zero” - any further CO₂ emissions due to human activity would then have to be matched by deliberate removal of CO₂ already in the atmosphere, including by planting trees. Net zero would have to occur by around 2075 to meet a 2℃ target.

Many illustrations are given for the difference between 1.5℃ and 2℃ worlds. At 1.5℃, summertime Arctic sea ice is projected to disappear once per century, compared to once per decade at 2℃; 8 per cent of plants that have been studied would lose half their climatically-suitable area, compared to 16 per cent; sea level rise would be 10cm less (with 10m fewer people impacted at today’s population levels); and while coral reefs might decline by a further 80% at 1.5℃, they could virtually disappear at 2℃.

The report identifies various routes by which emissions cuts would limit warming to 1.5℃; each makes assumptions about future changes in, for example, economic strategy, population growth and the rate at which low carbon energy is adopted. The IPCC recognises the challenges are “unprecedented in scale” but notes, for example, “the feasibility of solar energy, wind energy and electricity storage mechanisms have substantially improved over the past few years”.

The report is sensitive to the fact that changes required to meet 1.5℃ must be consistent with the UN’s wider sustainable development goals. Limiting climate change will help meet goals associated with health, clean energy, cities and oceans. But there are potential negative impacts on others (poverty, hunger, water, energy access) “if not carefully managed”.

So where next? Of course, the conclusions will be widely debated at many levels, but eyes will be on the UNFCCC’s response at its next meeting, in Katowice, Poland, in early December.

The Conversation

Keith Shine, Regius Professor of Meteorology and Climate Science, University of Reading.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

 
 
 
 

A helpful and informative guide to London, for the benefit of the New York Times editorial board

The sun rises over quaint old London town. Image: Getty.

It’s like with family members you hate: it’s fine for you to slag them off, but if anyone else has, you’re up in muted, backhanded arms about it.

Yesterday, the world’s number one London fan the New York Times tweeted a request for experiences of petty crime in the city. This was met by a deluge of predictably on-brand snark, like “Sometimes people scuff my leg and only apologise once”, and “Dicks who stand on the left-hand-side of tube escalators”. This served the dual purpose of uniting a divided London, and proving to the NYT that we are exactly the kind of chippy bastards who deserve to constantly lose their phones and wallets to petty crime.

By way of thanks for that brief endorphin rush, and in hopes of leading things in a more positive direction, I’d like to offer the Times this uplifting guide to London, by me, a Londoner.

I take my London like I take my coffee: on foot. If you are with someone special, or like me, like to reimagine your life in the format of Netflix dramady as you walk alone on Sundays, I can highly recommend the Thames Path as a place to start.

Kick things off next to Westminster, where we keep our national mace in the House of Commons. Useful though the mace might prove in instances of street theft, it is critical that it is never moved from the House. It acts as a power source for our elected representatives, who, if the mace is moved, become trapped in endless cycles of pointless and excruciatingly slow voting.

Cross Westminster Bridge to the Southbank, where in the manner of a spoiled 2018 Oliver Twist, you can beg for a hot chocolate or cup of chestnuts at the Christmas market for less that £8. Remember to hold your nose, the mutton vats are pungent. Doff your cap to the porridge vendor. (LOL, as if we make muttons in vats anymore. Box your own ears for your foolishness.) Then buy some hemp milk porridge, sprinkle with frankincense and myrrh, and throw it at the pigeons. There are thousands.

In the spring, head a little further south through Waterloo station. If you pass through the other side without getting ABBA stuck in your head, Napoleon’s ghost will appear to grant you three wishes.

Proceed to the Vaults, which is like the rabbit warrens in Watership Down, but for actors and comedians. No-one knows the correct way in, so expect to spend at least 45 minutes negotiating a series of increasingly neon graffiti tunnels. Regret not going to art school, and reward yourself upon your eventual entry with a drink at the bar. Browse the unintelligible show programme, and in no circumstances speak to any actors or comedians.

When you emerge from the Vaults three days later, turn back towards the river and head east. Enjoy the lights along the Thames while you pick at the spray paint stains on your coat. 


After about 20 minutes, you will reach the Tate Modern, which stands opposite St Paul’s Cathedral. Close to sunset, the sky, water, and cathedral might turn a warm peach colour. The Tate remains grey, coldly confident that for all its brutalist outline, it was still fantastically expensive to build. Feel grateful for that loose knit jumper you stole from the Vaults, and go inside.

Spend two minutes absorbing the largest and most accessible art, which is in the turbine hall, then a further hour in the museum shop, which is next to it. Buy three postcards featuring the upstairs art you skipped, and place them in your bag. They will never see the light of day again.

Head further east by way of Borough Market. Measure your strength of character by seeing how many free samples you are prepared to take from the stalls without buying anything. Leave disappointed. Continue east.

At Tower Bridge, pause and take 6,000 photos of the Tower of London and the view west towards parliament, so that people know. Your phone is snatched! Tut, resolve to take the embarrassment with you to your grave rather than shame Her Majesty's capital, and cross the river.

On the other side of the Bridge, you could opt to head north and slightly east to Shoreditch/Brick Lane/Whitechapel, where you can pay to enjoy walking tours describing how some pervert murdered innocent women over a century ago.

Don’t do that.

Instead, head west and north. through the City, until you reach Postman’s Park, which is a little north of St Paul’s, next to St Bartholomew's hospital. Go in, and find the wall at the far end. The wall is covered in plaques commemorating acts of extraordinary and selfless bravery by the city’s inhabitants. Read all of them and fail to hold back tears.

Then tweet about it.