IF you live in Brisbane, Perth or Darwin, then the year 2042 could be the year when your climate is shoved beyond anything humans there have ever likely experienced before.

From that point onwards, at least according to a new study in the leading science journal Nature, even the coolest years will be hotter than any record breaking scorchers you or your relatives might have experienced over the last 150 years or so.

For Sydneysiders, the study finds this "timing of climate departure" comes around four years earlier, in 2038. People in Canberra and Melbourne get 2045 as the year when their climate "shifts beyond historical analogues". Adelaide catches up in 2049.

For the entire globe, the year 2047 is the point when annual average temperatures move permanently outside modern day boundaries, according to the study.

All these dates are dependent on what the world does about its growing emissions of greenhouse gases that mainly come from burning fossil fuels, making cement and clearing land and forests. If there are no genuine moves to cut emissions, then the study claims these are the years we can look forward to.

If action is taken and emissions are quickly stabilised (no genuine sign of that at the moment), then the climate threshold in our Australian cities is crossed between 24 and 31 years later, depending on where you live. For the globe, stabilising emissions means the threshold is crossed 22 years later, in 2069.

Lead author Camilo Mora said of his study:

The results shocked us. Regardless of the scenario, changes will be coming soon. Within my generation, whatever climate we were used to will be a thing of the past.

To carry out the study, the 14 authors from the University of Hawai'i used 39 different computer models of the earth's climate system. They used the models to first recreate the years 1860 to 2005, and to then project into the future.

To check that the models were recreating temperatures, they checked the computer results between 1986 and 2005 against actual observations. They closely matched. The authors conclude:

Our results on the projected timing of climate departure from recent variability shed light on the urgency of mitigating greenhouse gas emissions if widespread changes in global biodiversity and human societies are to be prevented.



As my fellow The Guardian environment blogger John Abraham writes in his look at the research:

As this study shows, and other studies reinforce, many of the climate changes are already baked into the system. Even if we take significant and meaningful actions, many of the deleterious impacts will occur anyway.



But as if the warnings from the report are not stark enough, the researchers say that when you drill down into the locations where the climate system departs from the historical norms, the places hit earliest also happen to be the places where most of the world's biodiversity hotspots exist. The study finds:

The earliest emergence of unprecedented climates in the tropics and the limited tolerance of tropical species to climate change are troublesome results, because most of the world's biodiversity is concentrated in the tropics. We found that, on average, the projected timing of climate departure in marine and terrestrial biodiversity hotspots will occur one decade earlier than the global average under either emissions scenario.

For example, the study looked at the world's most species-rich areas for coral reefs, mangroves, seagrasses, marine reptiles, fish, plants, land mammals, land birds, marine mammals, amphibians and reptiles. They found that in every instance, the climate steps permanently away from the historic average in these areas five years or earlier than the global average.

Coral hotspots were hit the earliest of those studied, with the climate departing from the norm in the year 2050, even if emissions are stabilised, or 2034 if they're not. When the researchers looked at the acidity of the world's oceans, they found that the computer models showed oceans had already shifted outside anything seen between 1860 and 2005. That shift happened in 2008.

In a press release, Ken Caldeira of the Carnegie Institution for Science's Department of Global Ecology, who was not involved in the study, commented:

This work demonstrates that we are pushing the ecosystems of the world out of the environment in which they evolved into wholly new conditions that they may not be able to cope with. Extinctions are likely to result.

But perhaps the most startling figure presented in the study, is the number of people who currently live in areas where the climate will "exceed historical bounds" by 2050.

Depending on how the world's population grows and where, in the year 2050 there will be between one billion and five billion people living in places where the climate has permanently shifted. The authors also point out that the places earliest hit, tend to be those which are financially the poorest on the planet. The authors conclude: