In private conversations, many climate scientists express far greater concern at the progression of global warming and its consequences than they do in public, writes Dr Andrew Glikson.

In an article titled When the End of Human Civilization Is Your Day Job, a reference to a study by the University of Bristol cites, "Climate scientists have been so distracted and intimidated by the relentless campaign against them that they tend to avoid any statements that might get them labelled 'alarmists', retreating into a world of charts and data."

An analogy comes to mind of a medical team advising distressed relatives of the prognosis of a cancer patient, indicating a possible remission should the patient cease smoking. Some of the relatives plunge into depression but some criticise and attack the doctors, aided and abetted by the tobacco industry.

It is not uncommon to hear people criticising climate scientists for not telling them more about the climate, although when they are told, many recoil.

By contrast, in private conversations many climate scientists express far greater concern at the progression of global warming and its consequences than they do in public.

There is more than one answer to this question.

For one, they do. A number of prominent climate scientists, mostly representing the scientific consensus on climate change documented by the IPCC, have tried their best to convey the message in public forums. These scientists are mostly shunned by the conservative media which commonly offers platforms for those who do not accept the scientific evidence and the basic laws of nature.

2015 was Planet Earth's warmest year since modern record-keeping began in 1880, according to a new analysis by NASA's Goddard Institute for Space Studies. Global temperature in 2015 was +1.13 relative to the 1880-1920 mean. ( Data and overlay: NASA/JPL, Sunset image: daulon/Shutterstock.com )

A sizable group of climate scientists tends to regard the IPCC-based climate consensus as too optimistic.

However, mostly these scientists tend to be shunned by the media, as stated by Chomsky:

It's interesting that these (public climate) debates leave out almost entirely a third part of the debate, namely, a very substantial number of scientists, competent scientists, who think that the scientific consensus is much too optimistic. A group of scientists at MIT came out with a report about a year ago describing what they called the most comprehensive modelling of the climate that had ever been done. Their conclusion, which was unreported in public media as far as I know, was that the major scientific consensus of the international commission is just way off, it's much too optimistic ... their own conclusion was that unless we terminate use of fossil fuels almost immediately, it's finished. We'll never be able to overcome the consequences. That's not part of the debate.

Some glaciologists and Arctic scientists consider the accelerated rate of glacial melt in Greenland and West Antarctica may result in little remaining ice over these terrains toward the end of the century, leading to sea level rise on the scale of many meters, with catastrophic consequences for coastal and river valleys population centres.

In particular, Arctic scientists are concerned with rising methane levels rising from 1.76-1.82ppm to 1.81-1.86 ppm during 2000-2014.

The Arctic Ocean contains vast amounts of carbon accumulated during the Pleistocene ice ages. The greenhouse effect of methane traps up to 100 times more heat in the atmosphere than carbon dioxide within a 5 year period, and 72 times more within a 20 year period.

Atmospheric methane levels as measured at the Mauna Loa Observatory. ( source: NOAA/ESRL )

Scientists who study the history of the atmosphere-ocean system are worried by the unprecedented rate at which atmospheric CO2 levels are rising (i.e. by ~2 ppm/year, having reached 401.85 ppm by December 2015 - the highest level since at least 2.6 million years ago when the Arctic was ice free).

The current CO2 level and growth rate threaten an irreversible shift in the state of the Earth climate through looming tipping points, including an intermediary sharp cooling induced by flow of cold water into the oceans from Greenland.

There is little evidence that climate science had much to do with the outcomes of the Paris conference. The warming target of <1.5C has already been breached over the continents and a global ~2C temperature rise is only masked by the reflective albedo of transient sulphur aerosols.

Little account appears to have been taken in Paris of the time factor, if the decision to review the agreement every five years is considered.

At the current rate of ~2 ppm/year, CO2 will rise by 10 ppm closer to the stability threshold of the polar ice sheets.

Little encouragement can be gained from the non-binding promises emerging from the Paris conference, which James Hansen described as a "fraud". The unbearable knowledge, that global warming to 3 and 4 degrees C can only spell the demise of numerous species and a collapse of civilisation as we know it under extreme global temperatures, casts a shadow on day-to-day life.

Climate scientists are no longer alone in having to cope with the global emergency, whose implications have reached the defence establishment, yet the world continues to spend near to $1.8 trillion each year on the military, a resource that needs to be diverted to the protection of life on Earth. As the portents for major conflicts - in the China Sea, Ukraine, and the Middle East are rising - who will defend the Earth?

The new NASA global data set combines historical measurements with data from climate simulations using the best available computer models to provide forecasts of how global temperature (shown here) and precipitation might change up to 2100 under different greenhouse gas emissions scenarios. ( Credit: NASA )

There is a heavy price to be paid for those who alert the public to dangers against collective optimism since, even though the alarm is based on hard evidence, such people are denounced as alarmists, scaremongers, including such accusations as "pagan emptiness".

In a rare twist of the facts, climate scientists are referred to as 'warmists', even though what they do is the opposite, warning the world against GHG-triggered global warming.

Scientists have lost employment in government and other institutions. Scientists have been abused and threatened, and continue to face potential Royal Commissions and Congressional inquiries, constituting McCarthy-type witch hunts by those who deny the science.

Perhaps worst are the personal effects on, and responses, by people immediately associated with scientists, including friends and family. Many, already aware of the progression and dangers posed by global warming, and who experience climate change fatigue, are reluctant to follow the gory details. Going downtown, caught by traffic jams, walking through the malls, watching school children apparently unaware of the risk to their future, reflecting on the criminal consequences of saturating the atmosphere with carbon and on the lies propagated by those who do not accept the scientific method - climate scientists despair from expressing the unthinkable.

Dr Andrew Glikson is an Earth and paleo-climate scientist, visiting fellow at the Australian National University, Research School of Earth Science, the School of Archaeology and Anthropology, and the Planetary Science Institute, and a member of the ANU Climate Change Institute.