Climate Change Earth Science Environment

Embrace a Hot Earth

If the past is a key to the present, then we need to embrace a “Hot Earth.” In total, the earth has spent about 670 million years out of its 4.5 billion year history in glacial periods. So, glacial periods account for 15% of the earth’s existence.  The corollary is that the normal state of the planet is a hot, mostly ice-free planet. This normal, ice-free earth supports large inland seas and vast areas of the continental coasts are underwater. Houston, Miami, New Orleans, Charleston New York, Boston, and Washington DC are all sites for scuba diving in an ice-free world.

Our view of what’s normal stems from the fact that Homo sapiens have evolved during one of the relatively rare glacial periods in the earth’s history. This particular period began about 34 million years ago. So, from a human standpoint, global warming pushes us from a normal ‘cool earth’ state towards an unwelcome ‘warm earth.’ However, from a geological perspective, global warming is moving us back to the earth’s normal warm state.

The fact that a warm planet is normal does not provide humans with any comfort because approximately 33% of the world’s population lives within 100 meters of sea level. An ice-free earth submerges the first 66 of those 100 meters under the ocean. While this should give us pause for thought, it does not describe the greatest threats that climate change might bring. These will be threats to the oceans.

Hot earth of the past

We can peek back into the planet’s geological history to get a view of what hot earth looks like. The waning days of the dinosaurs set the stage for a hot world. For 66 million years, from about 100 million years ago to 34 million years ago, the earth’s average temperature was over 6 °C (10 °F) higher than at the end of the 20th century. At one point, about 50 to 55 million years ago, the average global temperatures spiked about 15 °C (25 °F) higher than today. Greenhouse gas concentrations like CO2 and methane were also much higher than today.

Polar ice did not exist during this hot earth period, and glaciers in high mountains disappeared. The planet earth was awash with water.  Pangea, the supercontinent, had already fragmented, and most of the continents had similar shapes to today. Also, many of these continents were punctuated and divided by shallow inland seas. 

North America was split into two pieces; the midcontinent and the West Coast. An inland seaway that ran the length of the continent from the Gulf of Mexico to the northern tip of Canada separated these landmasses.

Climatic conditions in the late Cretaceous allowed tropical plants to flourish in the polar regions. The temperature difference between the tropics and the poles was low compared to today. This lower temperature differential had a profound effect on atmospheric and oceanic circulation. 

Circulation patterns

Today, robust polar vortex systems, at each of the poles, create mid and high latitude air currents like the jet stream. These winds are responsible for much of the weather we experience daily. They also generate a variety of surface currents in the earth’s oceans.

The lack of strong temperature gradients between the equator and poles created a Cretaceous/Paleocene earth where seasonal changes were less pronounced. Also, the earth’s capacity for transporting heat from the equator to the poles significantly declined. Thermohaline circulation in the earth’s oceans was reduced or eliminated, and currents like the North Atlantic Gulf Stream ceased to exist. 

Weakened ocean currents and reduced atmospheric circulation had a knock-on effect on the ocean’s chemistry. Oceans today enjoy a high rate of “turnover” where dense water from the ocean’s surface sinks and deep ocean water upwells to the surface. This process keeps the oceans oxygenated.  

Black shales

The disruption of vigorous ocean turnover during the late Cretaceous led to the development of anoxic conditions in the deep oceans. This period of anoxia appears in the geological record as thick black shales. Oxygen-dependent life forms in the deep oceans disappeared, and black shales accumulated across the globe.

The Cretaceous atmosphere was rich in carbon-based greenhouse gases that helped sustain a warm planet. The black shales provided a carbon store that served to remove CO2 and methane from the Cretaceous atmosphere and fix that carbon in ocean-bottom sediments.

Today, black shales from the Cretaceous are a prolific source of oil in our modern society. These ancient shales were buried deep in the earth, where heat and time transformed their organic components into liquid oil. 

In a twist of irony, we are now burning that ancient carbon and releasing the Cretaceous greenhouse gases back into the atmosphere. So, an ancient hot world is helping humans propel themselves into another period of warm climatic conditions.  

Delusion on both ends of the spectrum

The voices on news and social media that decry the falsehoods of climate change and global warming are clearly a bit self-delusional. Warming is happening, and it is human-made. Thus far, earth’s governments have not fully come to grips with either of these facts. 

On the other hand, the voices arguing that we can stop global warming at a 1.5°C rise are also deluding themselves. As a society, we must think beyond the crisis and conjure up a vision of the future where our grandchildren inhabit planet earth and enjoy a rich quality of life. A ‘Hot Earth’ is coming, what shall we do about it?

It is true, as many climate change skeptics point out, that the earth has been warming and cooling for 4.5 billion years. What makes modern climate history different is the rate of change. Starting at the end of the last Ice Age, the average global temperature increased about 6°C, over a period of about 10,000 years, a 0.6°C per 1000 years rate of increase. Over the past 50 years, the rate of temperature increase had been equivalent to 13°C per 1000 years. The rate of change does matter.

The planet really is warming

The vast majority of scientific studies available today agree that global warming is real and that it is from greenhouse gases generated by human activity. The industrial revolution was in full swing by 1830. However, for the 10,000 years before the industrial revolution, the atmospheric CO2 levels held steady between 260 – 290 parts per million (ppm). But, between 1830 and 1950, atmospheric CO2 moved up to 310 ppm. Since 1950, it has risen to 411 ppm. This rise represents a 50% increase from the beginning of the industrial revolution.

Human nature being what it is, some groups of people still argue that the earth is flat. Public response to climate change is somewhat the same. Many people never bother to look at the data supporting the link between human activity and climate change. Others are not capable of processing and understanding that data. However, the vast majority of those denying climate change do so for the same reason that some people insist the earth is flat; it supports a world view that they wish to be accurate, despite all evidence to the contrary. 

Let’s stop it now

At the other end of the spectrum, we have various groups grappling with how to stop global warming. The 2015 Paris Climate Agreement included nearly 200 countries and set ambitious goals. The basic agreement was limiting the increase in average global warming to 2°C above pre-industrial levels. The agreement also had a stretch goal of limiting the temperature rise to 1.5°C. These ambitious goals rely on an end to fossil fuel use before 2050. 

The scientific premise is fairly straight forward. Global warming results from increasing levels of greenhouse gases,  so limiting the level of greenhouse gases will limit the temperature rise. But the devil is in the details. 

In 2014 IPCC calculations said that limiting Co2-equivalent (CO2-eq) levels in the atmosphere to 450 ppm would give us a good chance of meeting the 2°C goal. The problem is that by 2018 NOAA reported that we were already at 496 ppm CO2-eq. 

For those not familiar with the term, CO2-eq is a measure of collective greenhouse gas concentrations translated into the warming potential of CO2 only. If actual atmospheric CO2 levels were 410 ppm and the CO2-eq level was 500 ppm, then we interpret that the warming potential of all gases other than CO2 is equal to a 90 ppm increase in CO2 levels.

We have missed the first goals

  At a very basic level, we have already surpassed the necessary conditions to limit warming to 2°C. There are, of course, other remedial actions that we could take like scaling up carbon sequestration. However, all such actions require a collective will to succeed. 

The USA is withdrawing from the Paris Agreement, and the USA government is actively attempting to suppress research and knowledge about climate change. Since the USA is the second-largest carbon emitter in the world, its absence from the Paris Agreement is a blow to any efforts to limit temperature rise. Environmental regulations are also being rolled back in countries like the USA and Brazil. An unprotected Amazon rain forest burned out of control last year.

The probabilities are decreasing that coordinated world efforts to tame greenhouse gas levels will succeed. The political will does not currently appear to exist. The responsibility for large emission reductions rests with the world’s major existing and developing industrial powers. This collection of quasi-democracies and authoritarian governments is not well suited for the tasks outlined in the Paris Agreement.

Setting aggressive goals is an excellent way to try and kickstart a process, but it is not a guarantee that those goals are achievable. Increasingly it appears that global temperatures will rise above the 2°C threshold. Beyond this level are tipping points where positive environmental feedback loops will take over and drive temperatures higher regardless of the actions taken by humans.

Tipping points: scientific and social

Understanding tipping points and what happens from rapid climate warming may be reflected in events from 55 million years ago during the Paleocene-Eocene Thermal Maximum (PETM). This event is one of the most dramatic known instances of rapid global warming in the planet’s history, second only to today.

Fifty-five million years ago, the average surface temperature of the earth spiked about 15 °C higher than our average temperature today. Earth’s temperature was already warmer than today at the start of the event, but even so, global temperatures increase by 5 to 8 °C over about 20,000 years. This warming was not a movement from a glacial temperature low. This temperature rise started from already warm conditions. A rapid drop in the pH of ocean waters accompanied this period of significant global warming. 

Ocean pH fell by 0.4 units during the PETM event. It doesn’t seem like much, but it represents over a 100% increase in acidity from the pre-PETM levels. The PETM changes occurred over 20,000 years at a rate of a 0.1 unit decrease in pH every 5,000 years.

For comparison, present-day climate warming has produced an associated ocean water pH decrease of 0.1 units in about 200 years, and about 70% of that drop occurred in the last 50 years. Earth’s average temperature increased about 1 degree Celsius over the same time frame. The rate of change in pH today is 25 times greater than during the PETM.

So, even though the PETM is a reasonable analog to help understand some aspects of rapid climate warming, it cannot provide an exact match to the hyper rate of change that the earth’s climate is currently undergoing. 

Agents of PETM warming

Studies of the PETM event identify rapid increases in atmospheric carbon levels (greenhouse gases) as the primary agent of change. There is no consensus as to the causes of the atmospheric carbon increase during the PETM.  However, speculative reasons include increased volcanic activity, the eruption of a massive kimberlite field, or methane release from ocean bottom hydrates. 

The rapidity, strength, and short life span of the PETM temperature spike is unusual. The unusual nature of this event is what makes it a useful comparison to today as earth experiences rapid warming and acidification of the oceans.  The methane hydrate explanation for a rapid temperature rise associated with the PETM is an interesting possibility since it mimics environmental feedback loops that are operative today.

Deep oceans

On the ocean bottoms, where temperatures are low and pressures are high, conditions are ripe for the formation of methane hydrates, or methane clathrates as they are also known. Large amounts of methane become trapped within water crystals to form a substance similar to ice. Large deposits of these clathrates exist today on the ocean floors, and the oceans 55 million years ago probably had the same types of deposits. 

Temperatures before the PETM were already significantly higher than today, and at some threshold temperature value, the clathrates destabilized and released significant amounts of methane into the atmosphere. Methane is a more potent greenhouse gas than CO2, and it traps heat 20 times more effectively than CO2. Any release of significant amounts of methane will create conditions that exacerbate climate warming to produce an abnormal temperature spike.

This is a positive feedback loop that takes hold at some threshold tipping point. Once a significant amount of methane releases into the atmosphere, it creates warming that then causes even more methane release, and so on. The cycle ends when all the available methane hydrates have released their frozen payloads into the atmosphere.

The Arctic carbon tipping point of today.

We live in the Anthropocene, the time of man. Conditions for climate warming exist today due to the addition of significant amounts of CO2 into the atmosphere from industrial development. Anthropocene studies show that levels of CO2, methane, and nitrous oxide (the three most significant greenhouse gases) were stable and unchanged for most of the past 2000 years. 

That steady trend broke in modern times, and from the industrial revolution to now, the amounts of CO2 and nitrous oxide in the atmosphere have increased by 50 percent. 

The earth currently has significant methane clathrates on the ocean floors, and on land. However, the most immediate agent for developing a positive feedback loop is the Arctic permafrost. The Arctic contains the largest reservoir of carbon on the face of the earth, and this carbon is in two forms; methane clathrates in the surface and near-surface soils and organic matter frozen into thick layers of Arctic soil.

The big thaw

As the Arctic permafrost thaws, the clathrates will release their methane, and bacteria will start feasting on organic matter in the soil. The byproduct of this bacterial party will be CO2 and methane. Currently, the earth’s atmosphere contains 850 gigatons of carbon. An additional 1,400 gigatons of carbon are in the Arctic, waiting patiently for release. The release of Arctic carbon will cause an accelerated rise in global temperature, which in turn further increases the rate of Arctic carbon release. This forms the positive feedback loop necessary for a rapid spike in the earth’s average temperature. The cycle continues until the Arctic carbon is used up. 

Additionally, there are other science-based tipping points that affect climate change. The physics is understood for these carbon release cycles, as are the conditions for limiting their effects. But, science is not the issue. 

This is not to say that science is unimportant. Scientific analysis and rigorous data collection are the backbones of intelligent decision making. The reality is, however, that most decisions made on climate change are not based primarily on science; they are based instead on politics. 

 Scientific tipping points are important, but social tipping points will be what makes a difference. 

Social change and politics

Decisions about climate change can’t be separated from the web of money, power, and social opinion that controls all political systems. Profit is a powerful motive, and vested interests who are protecting their financial assets have substantial influence. Money and politics go hand-in-hand, so actions that limit profits receive pushback from those that stand to lose money.

From the standpoint of limiting climate change, power translates into developing and implementing government policy. Money and financial leverage are strong influencers of political power, but so is social opinion in many countries. Political structures ultimately rely on sustaining support from the societies they govern. The degree to which social opinion influences a government varies across a spectrum of government types ranging from democracies to authoritarian regimes and dictators.

Without social pressure, most political leadership will continue to operate contrary to the science of climate change. The pressure from vested financial interests will continue to garner their support. Politicians do not necessarily have the intellectual bandwidth to review and understand the messages that scientific research presents. Without pressure from social unrest or dissatisfaction, many politicians are happy to stay on their current path. 

How will this pressure come, and is there a ‘social tipping point’ where governments will start to act?  The answer is not fully known, but clearly the recent rise of young climate activists is a step towards such change. 

Youth activism

There are reasons why the younger generation leads the way in demanding changes in our approach to the climate. It is the same reason a whole generation in the 1960s exploded in protest over the Vietnam War: survival. During the 1960s, the draft was in full force and the blind persistence of the government to fight a war it couldn’t win was a death sentence to many. 

Blind political persistence to take wealth today at the expense of the environment, and let future generations pay the price, probably does not seem like a great deal to today’s youth. Just as those politicians who start wars don’t die in them, those politicians who make poor environmental decisions today will not be the ones to suffer the consequences. 

Politics can work to move climate and environmental issues forward. Politics, however, is subject to the whims of those in power. It is is just as easy to move forward as backward. When science ceases to form a basis for policymaking and becomes a partisan political tool, then poor long-term decision making will be the rule of the day. The will of governments to address climate change, or not, is a tipping point. The only question is, which way will the scales tip.

In democracies, the individual’s power to vote is one of the most potent weapons in the arsenal of creating change. A younger generation fights against the apathy of the status quo. It is an uphill battle, and ongoing change will not wait while this conflict plays out slowly in real-time. For this reason, we must embrace hot earth. It is coming, and the world’s ability to stave off its effects is limited.

What does it mean to embrace hot earth?

Embracing a warmer planet is not a white surrender flag waving in defeat. Science does matter, and some things can be done to mitigate the effects of rapid climate change. But the underlying reality is that we have probably already moved past some of the critical environmental tipping points. Beyond these threshold points certain feedback loops will continue to drive long term change no matter what the world does. Along the margins of climate change, some human populations are already feeling the pinch and struggling to cope with their rapidly changing world. 

Maintaining and expanding forested areas and protecting wetlands are clear wins that increase carbon sequestration and counteract against increasing greenhouse gas emissions. Sustainable energy technologies reduce the burning of fossil fuels. If electricity from sustainable sources provides fuel to electric vehicles, then larger reductions in emissions will benefit our societies. Companies, communities, and individuals can creatively do their part, but it will not be enough. Without long term government policy to provide an economic framework for our collective future, we will fail. We will continue to utilize our current economic model for environmental pollution.

Economics of pollution

‘Pollution pays’ is the driving economic principle behind much of the environmental pollution we experience today. Superfund sites create a prime example of how this works. They showcase a process that provides a way to maximize profits at the expense of the general public in hopes that future taxpayers cover the cost for damages done.

During the last two decades, cleaning up superfund sites cost the American taxpayer over 21 billion dollars. The economics of how we got to this point are quite simple. 

If you are manufacturing a widget that sells for $100, and it cost you $50 to produce it, then you have a handsome profit of $50 per item. However, if producing that object creates toxic waste byproducts that require disposal, your profits suffer. 

If your business chooses to neutralize and dispose of those wastes in an environmentally responsible way, then the additional cost will be $40 per widget. Option two is to buy a large plot of land beside your factory and bury the waste below the ground. This option costs $10 per widget, so you choose the second option to maximize your profits. 

The $40 per widget cost to responsibly dispose of the toxic materials has not gone away; you have simply deferred it. When site cleanup occurs, the taxpayer picks up that cost. For many years Congress has declined to fund the needed cleanup of Superfund sites adequately. So the price is paid in another way by the 53 million people who live within three miles of a Superfund site. They struggle against higher incidents of health issues, including cancer and birth defects.

The economics of pollution rely on cost deferral-and-transfer to maximize present-day profits. The transfer of these costs is usually to future taxpayers.

The power of the vote

Within democracies, the power of the vote is the only force that can implement meaningful and long term change. Apathy is the biggest threat to such a movement. Large numbers of people use the past as their vision of the future. “Make America Great Again” is the poster child example of such a vision. Reverting to an idealized view of the past is the best vision that many can muster for the future. 

However, time does not run in reverse, and the past cannot be miraculously catapulted into the future. Life is not a static process, and humans have to embrace change to survive. Climate change is no different.  A hotter world is on its way, and we cannot stop it. We need to have a vision of how we will embrace the change and still maintain a world where our children can prosper and live full, productive lives. 

Those who want positive change must actively pursue it. Educate yourself on the facts. Engage with others in meaningful discussions, so you understand their point of view, and they understand yours. Know what you stand for and vote for your position at every opportunity. When enough people do this, we will have reached a social tipping point that can push society towards a future where humans can exist in a long term balance with the rest of the biosphere.


Cretaceous Period (National Geographic) –

Disturbing Animation Shows What Earth Would Look Like if All the Ince Melted (Fiona MacDonald – Science Alert) –

Hothouse Earth: our planet has been here before – here is what it looked like (The Conversation) –

What can the Cretaceous tell us about our climate? (Philip Pika – EGU Blogs) –

Four degrees of separation: lessons from the last Ice Age (Prairie Climate Central) –

Abrupt Climate change During the Last Ice Age (Matthew Schmidt & Jennifer Hertzberg – The Nature Education Knowledge Project) –

What is causing climate change?  (Committee on Climate Change) –

The Ups and Downs of Global Warming (NASA) –

CO2 Currently Rising Faster than the PETM Extinction Event (Rob Painting – Skeptical Science) –

Temperature and atmospheric CO2 concentration estimates through the PETM using triple oxygen isotope analysis of mammalian bioapatite (Gehler, Gingerich, & Pack – PNAS) –

How We Know Global Warming is Real (Tapio Schneider – Skeptic) –

Climate Change (Global Footprint network) –

Climate Change 2014 Synthesis Report Summary for Policymakers –

The NOAA Annual Greenhouse Gas Index (AGGI) –

Glossary: Carbon dioxide equivalent (Eurostat) –

When global warming made our world super-hot (Colin Barras – BBC) –

Smithsonian: Ocean – Find Your Blue

Constraining the evolution of Neogene ocean carbonate chemistry using the boron isotope pH proxy

The oceans are acidifying at the fastest rate in 300 million years. How bad could it get?

Ocean Acidification

Very large release of mostly volcanic carbon during the Paleocene-Eocene Thermal Maximum

A primer on pH

What are the greenhouse gas changes since the Industrial Revolution?

Huge amounts of greenhouse gases lurk in the oceans, and could make warming far worse (Todd Woody – National Geographic) –

Feature Photo: Upper Terraces of Mammoth Hot Springs (Photographer – Brocken Inaglory) – This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license –

Photo: Vote Here Sign (Jay Phagan) – This file is licensed under the Creative Commons Attribution 2.0 Generic license. –

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.