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.


The tube that’s not a tube: What exactly is the Northern City line?

State of the art: a train on the Northern City Line platforms at Moorgate. Image: Haydon Etherington

You may never have used it. You may not even know that it’s there. But in zones one and two of the London Underground network, you’ll find an oft-forgotten piece of London’s transport history.

The Northern City line is a six-stop underground route from Moorgate to Finsbury Park. (It’s officially, if confusingly, known as the Moorgate line.) But, unlike other underground lines, it not part of Transport for London’s empire, and is not displayed on a normal tube map. Two of the stations, Essex Road and Drayton Park, aren’t even on the underground network at all.

The line has changed hands countless times since its creation a century ago. It now finds itself hiding in plain sight – an underground line, not part of the Underground. So why exactly is the Northern City line not part of the tube?

The Northern City line, pictured in dotted beige. Source: TfL.

As with many so many such idiosyncrasies, the explanation lies in over a century’s worth of cancellations and schemes gone awry. The story starts in 1904, when the private Great Northern Railways, which built much of what is now the East Coast Main Line, built the line to provide trains coming from the north of London with a terminus in the City. This is why the Northern City line, unlike a normal tube line, has tunnels wide enough to be used by allow mainline trains.

Eventually, though, Great Northern decided that this wasn’t such a bright idea after all. It mothballed plans to connect the Northern City up to the mainline, leaving it to terminate below Finsbury Park, scrapped electrification and sold the line off to Metropolitan Railways – owners of, you guessed it, the Metropolitan line.

Metropolitan Railways had big plans for the Northern City line too: the company wanted to connect it to both Waterloo & City and Circle lines. None of the variants on this plan ever happened. See a theme?

The next proposed extensions, planned in the 1930s once London Underground had become the domain of the (public sector) London Passenger Transport Board, was the Northern Heights programme. This would have seen the line would connected up with branch lines across north London, with service extended to High Barnet, Edgware and Alexandra Palace: essentially, as part of the Northern line. The plans, for the main part, were cancelled in the advent of the Second World War.

The Northern Heights plan. The solid green lines happened, the dotted ones did not. Image: Rob Brewer/Wikimedia Commons.

What the war started, the Victoria line soon finished. The London Plan Working Party Report of 1949 proposed a number of new lines and extensions: these included extension of the Northern City Line to Woolwich (Route J) and Crystal Palace (Route K). The only one of the various schemes to happen was Route C, better known today as the Victoria line, which was agreed in the 1950s and opened in the 1960s. The new construction project cannibalised the Northern City Line’s platforms at Finsbury Park, and from 1964 services from Moorgate terminated one stop south at Drayton Park.

In 1970, the line was briefly renamed the Northern Line (Highbury Branch), but barely a year later plans were made to transfer it to British Rail, allowing it to finally fulfil its original purpose.

Before that could happen, though, the line became the site of a rather more harrowing event. In 1975, the deadliest accident in London Underground history took place at Moorgate: a southbound train failed to stop, instead ploughing into the end of the tunnel. The crash killed 43 people. The authorities responded with a major rehaul of safety procedure; Moorgate station itself now has unique timed stopping mechanisms.

The last tube services served the Northern City Line in October 1975. The following year, it reopened as part of British Rail, receiving trains from a variety of points north of London. Following privatisation, it’s today run by Govia Thameslink as part of the Great Northern route, served mainly by suburban trains from Hertford and Welwyn Garden City.

Nowadays, despite a central location and a tube-like stopping pattern, the line is only really used for longer-scale commutes: very few people use it like a tube.

Only 811,000 and 792,000 people each year enter and exit Essex Road and Drayton Park stations respectively. These stations would be considered the fifth and sixth least used in the tube network – only just beating Chorleywood in Hertfordshire. In other words, these usage stats look like those for a station in zone seven, not one in Islington.

One reason for this might be a lack of awareness that the line exists at all. The absence from the tube map means very few people in London will have heard of it, let alone ever used it.

Another explanation is rather simpler: the quality of service. Despite being part and parcel of the Oyster system, it couldn’t be more different from a regular tube. The last (and only) time I used the line, it ran incredibly slowly, whilst the interior looked much more like a far-flung cross-country train than it does a modern underground carriage.

Waiting for Govia. Image: Haydon Etherington.

But by far the biggest difference from TfL is frequency. The operators agreed that trains would run between four and six times an hour, which in itself is fine. However, this is Govia Thameslink, and in my experience, the line was plagued by cancellations and delays, running only once in the hour I was there.

To resolve this, TfL has mooted taking the line over itself. In 2016, draft proposals were put forward by Patrick McLoughlin, then the transport secretary, and then mayor Boris Johnson, to bring "northern services... currently operating as part of the Thameslink, Southern and Great Northern franchise" into TfL's control by 2021.

But, in a story that should by now be familiar, Chris Grayling scrapped them. At least it’s in keeping with history.