We know that sustainable development has an environmental component, and three of the SDGs numbers 13, 14, and 15 deal directly with the kind of environment we want to maintain on Earth. So let's consider human interactions with the environment. We often hear it claimed that we're living in the Anthropocene, a term that loosely translates to The Age of Humans. Paul Crutzen, who was one of the three chemists awarded the Nobel Prize for discovering that human activities were impacting the ozone layer around the Earth, introduced the term in the early 2000s. Geologists have assigned names to each period in the Earth's history on the basis of the characteristics of the layers of the Earth that accumulated during that period. What Crutzen was arguing by suggesting that we now live in the Anthropocene was at the layers of Earth accumulating now contains such a strong signal of human activities as to be clearly distinguishable from the layers that accumulated for example, only a few hundred years ago, and that the differences between the new layers and the old layers are great enough to warrant identifying current time as a new geological phase or a period in the Earth's history. Geologists are still deliberating if the case is strong enough to warrant an official name change of the period in which we are living. Regardless of the outcome of those deliberations however, there can be no doubt that human activities are leaving a very clear signal in the Earth's stratigraphic record, that is to say in the layers accumulating on Earth. We see this with the remains of new human made materials such as plastic, cement, synthetic fibers, and other new to the earth chemicals and materials in the layers of Earth. The human signal is also obvious in what will ultimately become the fossil record as there are now far more domesticated than wild animals on earth, and even our domesticated animals are changing through time. Modern humans emerged two to 300,000 years ago, and of course have left remains of their activities behind in the fossil record over that entire period. It's during the last century however, that the human signal has become so strong at the global level. Owing to increasing population, increasing wealth, and new technologies, there's been a tremendous increase in the human endeavor. Here, we see the development of a number of proxies for human activity plotted for the time period 1750 to 2010. All of these, world population, GDP, foreign investment, people living in cities, use of energy and fertilizers, damming of rivers, use of fresh water, production of paper, transportation, telecommunication, and international tourism show an enormous increase since about the 1950s. And we call this period "the period of Great Acceleration." The Great Acceleration is mirrored in various proxies describing the state of the Earth's system at the global level. Greenhouse gases, CO2, methane and laughing gas, depletion of the ozone layer, temperature near the Earth's surface, acidification of the ocean, capture of marine fish, farming of shrimp in Southeast Asia, input of reactive nitrogen to coastal waters leading to oxygen depletion, the felling of tropical rainforest, the conversion of natural ecosystems to farming land, and the loss of terrestrial biodiversity. That the curves describing human activities and the Earth system features resemble each other does not necessarily imply that two things are connected. However, careful study has documented that the changing signals recorded in the Earth features can largely be attributed to human activities. Such studies have led scientists to recognize that the earth operates as a self-contained system comprised of interacting physical, chemical, biological, and human components. And that is the sum of these interactions that determine the state or environmental conditions of the planet as a whole. There's first been widespread recognition of the fact that human activities in the Earth's system can have an influence at the planetary level in connection with the growing scientific understanding of climate change. What we call climate is simply the average weather conditions at a given location. Weather, and therefore climate are controlled by the amount of heat stored near the Earth's surface where this heat is stored, and how it is transported around the planet, and its interactions with the water found near or on Earth. The amount of heat stored near the surface of the Earth is a function of how much of the sun's energy arrives at the earth's surface, and how much of that heat then radiates from the Earth and back into space. Climate change then is the result of the change in this balance of heat in, heat out at the surface of the Earth. Lots of factors influence this balance, but one of the most important and certainly the one that has changed most in recent years is the concentration of what we call greenhouse gases in the atmosphere. Of these, CO2 is the most important, but there are several others including methane, and nitrous oxide or laughing gas, but also are generated through human activities. These greenhouse gases absorb the heat that's leaving the Earth's surface and essentially trap it near the Earth. This greenhouse effect around the Earth and other planets has been known since the early 1800s. Without it, the Earth would be very much colder than it is today. Data from ice cores have shown that throughout the Earth's history, there has been a clear relationship between greenhouse gases and temperature. The more greenhouse gas in the atmosphere, the warmer the temperature, and vice versa. Already in 1896, the Swedish Chemist Svante Arrhenius predicted that the release of CO2 from the burning of coal would lead to global warming. In 1992, the United Nations established the framework convention on climate change, UNFCCC, through which the global community is striving to gain control over human-caused climate change. Through the Paris Agreement of 2015, the 194 member countries of the UNFCCC have agreed a goal of holding human-caused global warming to well below two degrees above the average temperatures at the time of the industrial revolution. Gaining this control over climate change is a prerequisite for a number of SDGs and go 13 explicitly addresses this challenge. Under the UNFCCC is a scientific panel, the IPCC, that is charged with assessing all available scientific information concerning the potential human interaction with the climate. IPCC stands for Intergovernmental Panel on Climate Change, that the panel is intergovernmental means that it is countries themselves that nominate the scientists who populate the panel. Likewise, the member governments to the convention have to approve the reports of the panel before they are released. The IPCC in its latest report concluded, that there is greater than 95% certainty that humans have caused over half of the global warming recorded in recent decades. I recently spoke with Jens Hesselbjerg Christensen, who is a professor in Meteorology at the University of Copenhagen and the member of the IPCC, about climate change and the work of the IPCC. Since you are a member of the IPCC, can you tell me why is it that the IPCC is so convinced that much of the climate change we're seeing at the moment is actually caused by human activities? The evidence is compelling. The evidence from observations, from theories and from modeling simply rules out any other explanation. Only caveats that there might be things that we have totally overlooked. And that's always the caveat that comes into all bits of science is that's evolving. But the other factors are so clear that there's no way around it. Why do you think then? I mean given that the IPCC is made up of the scientists that have been identified by around 200 countries, what is it so many people still really don't believe the science? Now unless you really relate to it, work with it, it seems very distant, and then any other opinion may just be as important as the science. And I think this is a very fundamental way of dealing with knowledge. What is society risking if we don't get control over human perturbation or human effects on the climate system? So the whole alarming Bill that rings is that by turning on the heat of this planet, we reach a stage of the weather phenomena, and risks for droughts, and floodings that far exceeds what we experience so far. And on top of that with even modest degrees of warming, we will see sea level rise. And, in reality, probably several meters in the coming centuries. This would jeopardize the way of life that we know and, of course, with all kinds of other developments, you may ask, of course, we can adjust to this but if we are not planning it, we will be overwhelmed by the challenge to adopt. So what you're saying is that we have a garbage dump for our greenhouse gases in the atmosphere, and if we can. We know if we want to keep within two degrees, human caused climate change to within two degrees or warming to within two degrees, that we know how big that garbage dump is and that garbage dump is we can say, how much it's filled up, and we can say how much is left. And it's just a question of the longer we wait to close the gap, or to stop using it, the more drastic the changes have to be. Yes. It's clear that early action is simpler, possibly also cheaper. The longer we wait, we actually may pass the two degrees and that will be, of course, very problematic and very expensive to go down again. A lot of people say technology is going to save us and get out of this. What do you think about that? Technology is going to help us. It's not going to save us. We are the only ones who can save us. But, tell me, do you think it's really possible? Do you think that society will be able to hold global warming to within two degrees? We know it's doable. It's actually a question about resources, and money, and political will to do it. And I think that there is momentum now, and we have to give that hope into the future that that momentum is actually rolling the snowball and we will see things coming down the line. But right now, we can make a a green development that will be sustainable energy sources for the rest of the century. But, it's now within the next 10, possibly 20 years and it has to be really, really willing. We have the techniques in place. We know exactly what it takes. It's a question about preferences and priorities. And this is where we have the Paris Agreement established to work on this. That's the foundation for which we can achieve this. But, the window to close the gap and stay below two degrees is very small because if we are not really, very quickly adjusting our emissions and go in zero basically within the next 50 years, we will pass the two degrees. Can you explain the relationship between the Paris Agreement and the Sustainable Development Goals? Climate is a fundamental prerequisite from many of the Sustainable Development Goals. It's pretty clear that coping with the climate problem also have big implications in many of the other goals. And that's why it's a central task to deal with the climate crisis. It's easy to understand after talking with Yence. I'd so often argued that it's the climate SDG number 13 that must be addressed most urgently. The environmental concerns addressed in Agenda 2030 go, however, far beyond climate. That so many concerns are addressed, it's also what makes Agenda 2030 novel in the history of United Nations agreements. Until now, when these agreements have considered environmental issues, they've generally focused on a single problem or challenge, depletion of the ozone layer, introduction of contaminants to the environment, climate change, loss of biodiversity, and so on. Bringing concern for all of these challenges into one agreement and at the same time, linking these concerns to those related to the economic and social components of sustainable development is a logical consequence not only of the conclusions of the Brundtland Report but also of the recognition that human societies are an integral and important component of the Earth's system.