The Earth's climate has just hit an important milestone -- but it's not the sort of achievement we want.
The United Kingdom's Met Office announced on Tuesday (AEDT time) that global mean temperatures have reached one degree Celsius above the levels in the year 1900. A rise of two degrees is generally accepted among climate experts as catastrophic, potentially leading to sea level rises of one metre among a multitude of other environmental effects. Many climate agreements and emissions reductions goals set a two degree temperature rise as a marker point to be avoided.
So far in 2015, the Met Office reported temperatures had been recorded as 1.02 degrees higher than temperatures in the period between 1850 and 1900. The Office's projections forecast the trend will continue and hold true for the entirety of 2015, marking the first time the one degree threshold had been breached.
"We have seen a strong El Nino develop in the Tropical Pacific this year and that will have had some impact on this year's global temperature," said Stephen Belcher, Director of the Met Office Hadley Centre.
"We've had similar natural events in the past, yet this 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."
Amanda McKenzie, CEO of the Australian-based Climate Council, told The Huffington Post Australia that the globe was now halfway to what is an accepted measure of catastrophe, thanks to melting ice caps.
"The Greenland ice sheet, an enormous piece of ice sitting on land, is melting at a very rapid rate. Between one and two degrees rise in temperature, that ice sheet will reach a threshold where it will melt entirely," she said.
"That could be a 7m rise in sea levels -- not immediately, but over many years. That's 7m just from that ice sheet. We don't know where the threshold is, but that's the point -- we shouldn't be pushing the limits.
"We've hit one degree rise, that's a pathway to the absolute maximum. One of the most significant numbers in the global climate conversation is two degrees. We've all agreed we should stay under two degrees rise in warming. Pacific Islands say it should be under 1.5 degrees, because that rise would threaten their islands."
The dire warning comes just a day after Climate Central released a set of stunning visual projections showing what global iconic locations would look like after a two or four degree rise in temperatures. The Opera Bar outside the Sydney Opera House would disappear almost entirely if global temperatures rose by four degrees, with just the tips of sun umbrellas poking out of the water, while Shanghai, London, New York and Durban would almost disappear under huge water level rises.
McKenzie said while a one degree rise had taken more than a century, current projections showed that another rise to two degrees could happen within a generation.
"There are a range of projections, but one says that if left unchecked, we could be at two degrees by 2030. That's only 15 years away. It's up to us, as members of the global community, to reduce greenhouse gases and our use of energy," she said.
"We call this the critical decade. The decisions we make before 2020 will decide whether we hit those temperatures and see the increase in extreme weather. It depends on the decisions we make within the next five years."
McKenzie said the world was already experiencing the beginning effects of climate change, but that it was not too late to prevent the top-end worst-case scenario.
"There will be climate change. We're already experiencing climate change. Hot days are increasing and getting hotter, they are happening more often, and we're experiencing it all around the world," she said.
"Our actions will absolutely make a difference. The greater and quicker we act, the greater we'll benefit down the track. This is not just about future generations only -- it's about the current generations."