1. INTRODUCTION

We have in the past thought that our writing should always focus on our science. In part because we always have so much science to share and because this is what we have in common with our readers − the desire to solve some of the great questions and challenges of our world. Our opinions began to change somewhat at the 2013 Goldschmidt meeting in Florence. At a bar across from the Medici Chapel, over far too many beers, we were surrounded by a suite of students and postdocs, not asking details of our science, but trying to find out how we got to where we were, what motivated us, and how we got our ideas. This has been repeated again and again at subsequent conferences. Though we cannot, we suspect, really determine where our ideas come from, perhaps a bit of our background can provide some insight.

Quite curiously our backgrounds are very different, though in some ways this has always been our strength. Siggi grew up in Reykjavík and in rural Iceland, raising animals and shooting game. Eric grew up in New York City where the only farm animals were found in the refrigerator section of the local grocery store, and the only game animals in the local zoo. As a geochemist, Siggi’s background was largely field based and Eric’s largely computational and experimental based. The combination of our backgrounds, however, made it possible for us to go far beyond what either of us could do on our own.

Siggi: I was born and raised in Iceland. As a young boy, I spent summers at my grandfather’s farm in southeast Iceland, downstream from the glacier-covered Katla volcano. In the evenings, I would listen to stories of eruptions, ash falls and my grandfather galloping on his horse in front of the glacier’s outburst flood associated with the 1918 eruption of the Katla volcano. At the peak of the flood, it was the largest river on Earth. My interest in volcanoes and geology was kindled.

My high school teacher further inspired me to study geology at the University of Iceland. There I learned from Stefan Arnorsson and Sigurdur Steinthorsson about the power of thermodynamics, and how it helps to interpret water-rock interactions. After graduation in the spring of 1980, I took my first job as a geologist at the Nordic Volcanological Institute in Iceland, before heading to Johns Hopkins University for graduate school that fall. We got two eruptions that summer, and I was paid to study them. I spent my last week in Iceland on the slopes of the erupting Hekla volcano before my departure for the US in late August 1980. I took one day to pack and received a culture shock when I arrived for the first time in New York and then onwards to Baltimore. There I was to study gas buffers in basaltic geothermal systems with Hans Eugster at Johns Hopkins University. Hans was a great mentor, scientist, and artist. We had Friday seminars at his and Elain’s farm in Western Maryland, surrounded by his paintings. Elain, Hans’ wife, was a professor of mathematics at Goucher College in Baltimore. For my PhD thesis, I did field and laboratory studies of meteoric water-basalt interactions with Hans (Gislason and Eugster, 1987a,b; Fig. 1.1).

I had a few postdoc options in USA and Canada in 1985, but my wife Malla, an architect and urban planner, received an excellent offer from an Icelandic architectural firm, so I followed her back to Iceland and started working on a soft money post at the University of Iceland. I went back to Hopkins for few months during 1987, working with Dave Veblen on a TEM study of alteration products created during my low temperature PhD experiments. At the end of our stay at Hopkins in early autumn, we drove to Martha’s Vineyard where Hans and Elaine were building a summerhouse. When we left on the ferry, Hans waved for a long time, which was unusual for him. This was the last time I saw him, he died two months later from an infection, at the age of 62, virtually with his boots on.

Just before Christmas in 1987, the same day that Hans died, I got a permanent position at University of Iceland. Few years later in 1994, I went on a sabbatical to Toulouse, France, to work with Jacques Schott on dissolution rate experiments on moganite (a novel silica polymorph) and quartz. Peter Heaney, a Hopkins friend, had then recently shown that chalcedony and chert specimens from around the world contained a mixture of very small crystals of quartz and moganite. Chalcedony generally contains between 5 and 15 wt. % moganite, whereas chert from evaporitic environments may include more than 50 wt. % moganite. The aim was to define moganite’s dissolution rates and its thermodynamic properties (Gislason et al., 1997). On my first visit to the lab in Toulouse I ran into Eric Oelkers. Eric was and is direct, brilliant, honest, trustworthy and a lot of fun. We have been the very best of friends and collaborators from that day. My family and I were frequent visitors to Toulouse over the next 15 years and enjoyed the hospitality of Eric, Stacey, and Jacques. With PhD students and postdocs, we quantified the dissolution rates of volcanic glasses, climate control of weathering of basaltic rocks, the role of river suspended material in the carbon cycle and the effect of crystallinity on dissolution rates and CO₂ consumption capacity of silicates, as discussed in Section 2 of this volume.

The tide changed in 2007 with the beginning of the CarbFix project in Iceland. In February 2005 the Kyoto protocol entered into full force, committing countries to limit CO₂ emission. To address this challenge, the Icelandic President approached Eric and I, along with Einar Gunnlaugsson at Reykjavík Energy, Iceland, Wally Broecker at Columbia University, USA, to design a project, later referred to as CarbFix, to aid in limiting greenhouse gas emissions in Iceland. After nearly a decade of experiments, obtaining permissions and the preliminary injections, Reykjavík Energy and other members of CarbFix laid the foundation of industrial scale gas capture from concentrated gas streams and directly from the atmosphere, followed by injection and mineralisation at the Hellisheiði site in Southwest Iceland as described in Section 4.

Eric: I am proud to have been born and raised in the Bronx and to have grown up in New York City. Much of the surface of New York is covered in asphalt or large buildings, so this is hardly a hotbed of geology. In fact, it’s likely as far as one can get from the natural environment and still be on the surface of our planet. After graduating from schools with such catchy names as P.S. 203, I.S. 74, and Cardozo High School, I left home to study Chemistry at the Massachusetts Institute of Technology.

The defining moment convincing me to try geology occurred the summer of my first year at university. I had an internship at Southwest Specialty Chemicals in Deer Park, Texas. A memorable feature of Deer Park was that the colour of the sky was always a different shade of purplish grey each day. My job was to collect samples from trucks arriving with solvents, such as acetone and ammonia, and measure their purity. Apparently, a common practice at the time was to add water to these solvents diluting these down to the minimum spec. limit to maximise profits. If below the purchased quality I was to send the truck away.

This was boring work. So boring, I began to calculate the number of minutes left in my work day, every five minutes. Within weeks I was convinced that I could not be a career chemist. Upon returning to MIT, I took my first geology class, Introduction to geology taught by John Southard. This was fun. Visiting outcrops, hammering on rocks, and perhaps most important I was able to see scientific principles right in front of me in the field.

Not wanting to start work after graduation, I applied to a large number of graduate programmes, and despite having only average grades got into all of these. I decided to go to Berkeley, California. I recall my largest motivation was all of the California beach and surfing movies I watched as an adolescent, but for some reason Harold Helgeson seemed to think I moved to California to study geochemistry, so he offered me a research assistantship as part of his research group “Prediction Central” (see Fig. 1.2).

I regret that many of you reading this volume never had the chance to meet Helgeson. He was a classic “work hard, play harder” professor. Perhaps the closest person in personality to the character Morris Zapp in the book Changing Places by David Lodge. He was a generous and very loyal advisor, and he changed geochemistry by creating the mineral-fluid-gas thermodynamic database (Johnson et al., 1992). While there, Helgeson drove into our heads the minute details of thermodynamics and kinetics. Peter Lichtner, there at the time, introduced me to geochemical reactive transport modelling.

Geology, being cyclical, was out of favour when I graduated and jobs in the United States were scarce. My best opportunity was to move to France to work with Jacques Schott, an experimental geochemist working largely on mineral-fluid reaction rates. Jacques was far different in personality than Helgeson. Jacques is highly cultured, always curious, loves hiking, and always has time to discuss any scientific detail one has in mind. After two years I was recruited at the CNRS and I continue to work with Jacques to this day.

Funding experimental research, however, proved challenging, but the European Commission had the answer in the form of Research and Training Networks. All one needed to do was to organise a set of like-minded scientists located in different European countries and agree on a collaborative research and training programme. This turned out to be the path to great friends, great collaborators, and great science. Siggi and I gathered a close group of very motivated and talented geoscientists including Manolo Prieto (Spain), Vala Ragnarsdottir (UK and Iceland), Andrew and Christine Putnis (Germany), Susan Stipp (Denmark), Björn Jamtveit (Norway), Per Aagaard (Norway), Jordi Bruno (Spain), and Liane Benning (UK and Germany) who ran research and training networks together with more than 100 PhD students and postdocs since 1999. The keys to success of these networks were mutual respect and complete trust among us so we could share all of our ideas. Science can be a rough career. As is the case for all scientists, our work is commonly criticised, many of our grant proposals and papers are rejected, and most of our publications barely read. It is this group of friends and our students and postdocs that have kept us moving and motivated. It is only their encouragement and support that made it possible to continue pursuing scientific research over our careers.

When starting to develop this Geochemical Perspectives, we decided to focus on the global carbon cycle and how our understanding of the natural Earth surface might be used to limit future carbon emissions to the atmosphere. We chose to limit our attention to the natural and anthropogenically influenced carbon cycle, both because we have worked extensively in this area over the past two decades and to focus attention on the critical societal need to limit global warming in the coming decades. We hope that by creating this perspective we can inspire members of our community to help develop effective and large scale solutions to attenuate carbon dioxide emissions to our atmosphere, building on our knowledge of natural processes.

Interest in the connection between the CO₂ content of the atmosphere and global temperature goes back for over a century. Perhaps the first scientific report linking increasing CO₂ content to global climate was the study of Arrhenius (1896). Using model calculations, he concluded that the halving of the atmosphere’s CO₂ content could lead to an ice age, but doubling this content could increase global temperature by 5 to 6 °C.

Scientific efforts connecting atmospheric CO₂ content with global temperature accelerated beginning in the 1960’s. This acceleration was due to two major scientific efforts. First, beginning in 1957, Charles Keeling began measuring the CO₂ content of the atmosphere on Mauna Loa, Hawaii, and in Antarctica. By 1965, a clear temporal increase in atmospheric CO₂ concentrations was evident (Brown and Keeling, 1965; Pales and Keeling, 1965). At approximately this time, the first comprehensive compilations of the temporal evolution of global temperature were published by Mitchell (1963, 1972). Mitchell’s 1963 global temperature curve is shown together with several others in Figure 1.3. These studies showed that global temperature increased steadily from the 1880’s until approximately 1940, after which it decreased into the 1970’s. This apparent discrepancy was attributed primarily to the increase in aerosols in the atmosphere. Broecker (1975), in the first scientific study to use the expression “global warming”, concluded that the global cooling trend from 1940 to 1975 would soon come to an end. He concluded that the exponential increase in atmospheric carbon dioxide content would drive global temperatures beyond the limits experienced during the previous 1,000 years.

Scientific research over the following decade generated a unified view of the factors influencing global climate, including the role of greenhouse gases, aerosols, orbital forcing and solar radiation (Manabe and Stouffer, 1980; Hansen et al., 1981). The message was clear. Anthropogenic increases in atmospheric CO₂ concentrations could lead to a dramatic and rapid increase in global temperatures. This wake-up call motivated the United Nations to organise the first Intergovernmental Panel on Climate Change (IPCC) in 1988. Since that time the IPCC has delivered five assessment reports (https://www.ipcc.ch/reports/). In 1990, the First IPCC Assessment Report summarised climate change research and its global consequences. The Second Assessment Report in 1995 provided material leading to the adoption of the Kyoto Protocol in 1997. The Third Assessment Report, in 2001, outlined the likely impacts of climate change. The Fourth Assessment Report, delivered in 2007, laid the groundwork for a post-Kyoto agreement, focusing on limiting global warming to 2 °C. The Fifth Assessment Report was delivered in 2014 and provided the scientific input for the Paris Agreement. The Sixth Assessment Report is expected to be finalised during 2023. Each report is an extensive and informative review of the science of climate change and public policy.

The international impact of the IPCC has been great. This impact was further enhanced by a number of highly visible supporters, including Al Gore, the United States Vice President at that time (1993 to 2001), who gave a large number of presentations and created a popular film publicising the evidence for and the consequences of global warming. For their efforts the IPCC and Al Gore shared the 2007 Nobel Peace Prize. At the invitation of the President of Iceland, Siggi met Al Gore for a working dinner at President Grimsson’s residency in April 2008, and later in the year he met Rajendra Kumar Pachauri, the chairman of the IPCC in Iceland for an afternoon tea to discuss carbon capture and storage via the CarbFix method described in Sections 4.4−4.6.

One of the major ways to address the challenge of global warming is carbon capture and storage (CCS). Although the impact of the IPCC reports and international interest in arresting global warming was great, the number of operating, in construction and planned CCS facilities, as shown in Figure 1.4, peaked in 2011 and declined in terms of total CCS capacity by more than 50 % from 2011 through 2017. This decline was largely due to stopping projects that were in construction or planned. There are several reasons for this large drop in interest in CCS over these years, much of it due to a public misinformation campaign in part supported by the energy and electrical utility industry. This campaign was aimed at making the public suspicious of global warming and of the scientific community in general (Brulle, 2019; Franta, 2021). Some of this misinformation stems from the complexity of the controls on global climate. Notably, the link between CO₂ and global temperature has been controversial over the past several decades, as this link has not been direct over geologic time (Broecker, 2018). Moreover, the interpretation of various evidence has changed over time. For example, one of the figures shown by Al Gore in his film An Inconvenient Truth is reproduced in Figure 1.5. This figure shows what appears to be a strong correlation between an increase in global temperature and atmospheric CO₂ content. A subsequent and more detailed study of these ice core records shows that, in fact, the change in CO₂ concentrations lagged the change in temperature by approximately 800 years (e.g., Caillon et al., 2003). The simple explanation for this lag is the retrograde solubility of CO₂ in seawater. When global temperature is driven by orbital planetary cycles, an increase in ocean temperature decreases the solubility of CO₂ in seawater. This decrease in solubility leads to the exsolution of CO₂ from the oceans into the atmosphere and the CO₂ content of the atmosphere increases. The 800 year lag is approximately twice the residence time of dissolved CO₂ in the oceans, and close to the mixing time of the marine system.

Nevertheless, doubt originating from this lag between increasing CO₂ concentrations and global temperature rise and a global financial downturn, helped slow considerably the pace of CCS activities by the end of the decade. This slowdown was further reinforced by an incident referred to by the popular press at that time as “Climategate”. In November 2009, more than 1,000 emails among the scientists at the Climate Research Department of the University of East Anglia were stolen and made public (Leiserowitz et al., 2012). These emails included some that discussed how to best describe and present sensitive climate data to illustrate the extent of global warming. The publication of these emails was used to discredit the scientists as well as the whole scientific field of climate research. Others claimed that the emails invalidated the conclusions of the 2007 IPCC report confirming the Earth was warming due to anthropogenic activities. Although 1) nothing in the leaked emails contravened the evidence for global warming, and 2) to date the people responsible for leaking these emails have not been revealed, these emails were seized upon as evidence that scientists cannot be trusted, and that the whole of global warming was a hoax created by scientists to obtain attention and grant funding.

It is only over the past few years that the evidence for global warming has become so overwhelming that the mountain of misinformation has been overcome. As we are writing this section, during the summer of 2022, Europe is experiencing the hottest summer on record and experiencing an historic drought (Rousi et al., 2022). The effects of global warming are leading to extreme and destructive weather events worldwide (Thompson et al., 2022). The seven warmest years directly measured in history have occurred since 2015 (World Meteorological Organization, 2022). These events have altered dramatically public opinion in favour of addressing the challenges of CO₂ reduction and global warming. The change in public opinion helped motivate the development of financial incentives, including tax breaks for CCS and emission trading schemes. Together these more recent developments have motivated a resurgence in CCS research and industrial scale projects shown in Figure 1.4.