The UK’s Met Office has warned that data for 2015 so far indicates that the world is already halfway to the two-degree Celsius global warming limit.

Since the 1990s, some researchers have argued that the most serious consequences of global warming, such as flooding, extreme weather events, and drought, might be avoided if global average temperatures rise by no more than 2°C above pre-industrial levels.

It is expected that this limit will be the cornerstone of the new legally binding global climate agreement that will be discussed at the 2015 Paris Climate Conference, also known as COP21, in December.

However, the Met Office has revealed that data for 2015 has shown that, for the first time, global mean temperature at the Earth’s surface is set to reach 1°C above pre-industrial levels, largely due to human influence.

Humans driving climate into “uncharted territory”

Based on data from January to September, 2015 global mean temperature was shown to be 1.02°C above pre-industrial levels (1850-1900).

Stephen Belcher, director of the Met Office Hadley Centre, said: “[T]his is the first time we’re set to reach the 1°C marker and it’s clear that it is human influence driving our modern climate into uncharted territory.”

The Met Office added that early indications suggest 2016 will be similarly warm and said it “expects warming to continue in the longer term”.

It stated that keeping carbon dioxide emissions under 2900 gigatonnes would have a “likely” (more than 66 per cent) chance of limiting warming to below 2°C, but that as of 2014, about 2000 GtCO2 had already been emitted. This equated to around two-thirds of the 2°C budget.

Peter Stott, head of climate monitoring and attribution, said: “This year marks an important first, but that doesn’t necessarily mean every year from now on will be a degree or more above pre-industrial levels, as natural variability will still play a role in determining the temperature in any given year.

“As the world continues to warm in the coming decades, however, we will see more and more years passing the one-degree marker – eventually it will become the norm.”

The Met Office also noted that some of the impacts of global warming include sea-level rises, which have already risen by a global mean of 20 centimetres since pre-industrial times, around one-third of the level that could be seen by 2100 in a 2°C world.

Still possible to limit warming to 2°C

The Met Office highlighted research suggesting it is still possible to limit warming to 2°C above preindustrial levels. However, the later that global CO2 emissions peak, the faster subsequent emissions cuts would need to be in order to keep global temperature rise below the limit.

Picturing the effect of climate change in Australia

The Met Office report is one in a raft of global warming papers released ahead of COP21.

The World Meteorological Organization – the UN’s weather agency – has already warned that levels of carbon dioxide and methane, two key greenhouse gases, reached record highs last year, while five Australian papers (written for the annual extremes issue of the Bulletin of the American Meteorological Society) found that heatwaves are now almost 20 times more likely in Australia as a result of human caused carbon emissions.

Further, recent data showed that Australia just experienced its hottest October on record.

In an attempt to picture future effects of climate change, research organisation Climate Central has released a series of interactive images created by visual artist Nickolay Lamm that show how rising temperatures can affect the sea levels of some of the world’s most populous cities.

The pictures support the body’s Mapping Choices: Carbon, Climate, and Rising Seas — Our Global Legacy report, which warns that current carbon emissions could cause a 4°C rise in temperature by 2100, which could “lock in enough eventual sea level rise to submerge land currently home to 470 to 760 million people globally”.

It also highlights that reducing carbon emissions to levels within the proposed international target of 2°C warming could still affect 130 million.

Speaking of the images, co-author of the Mapping Choices report Dr Benjamin Strauss, said: “Long-term sea level rise set in motion by near-term carbon emissions threatens major coastal cities across the world. Here we present paired images showing how iconic locations — in London, Shanghai, Mumbai, Sydney, Rio de Janeiro, Durban and New York — could fare under scenarios of business as usual vs. a sharp transition to clean energy.

“[W]e show projections of post-2100 sea level rise that could be locked in following 4°C of warming from carbon pollution in the coming decades. This pathway corresponds roughly to business as usual… [We also] show projections based on 2°C of warming from carbon pollution. This degree of warming corresponds to the target limit widely discussed today as the threshold to avoid catastrophic climate change…

“In December, a major new round of global climate talks is being held in Paris. The decisions reached there may have a strong bearing on which of these two scenarios the future looks like most.”

Above is a virtual representation of how Sydney’s harbour would look if global warming increases by 4°C and 2°C. A video of how global warming could affect Melbourne can be viewed below.

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