Our Warming Planet

The following sections are included:

• Acknowledgements
• Contents
• Introduction

Key Points and Key Components

It all begins with the Sun. The global-mean solar illumination of the Earth has been determined to be about 340 W/m² of which about 100 W/m² is reflected back to space. Hence, the Earth absorbs a global annual-mean 240 W/m² of solar energy. This amount of energy is just sufficient to support a global-mean temperature of 255 K. However, the global-mean surface temperature of the Earth is known to be about 288 K, which implies that the Planck emission from the ground surface must be about 390 W/m². It is this ‘missing energy’ circumstance that led Joseph Fourier to conclude back in 1824 that there must be an atmospheric greenhouse effect causing thermal heat energy to be radiated downward from the atmosphere in order to supply the additional heat energy needed at the ground surface. This is because in the absence of the greenhouse effect, 240 W/m² of absorbed solar energy is not sufficient to sustain a surface temperature of 288 K…

Among many challenges, climate change research seeks to understand:

• how and why Earth’s atmosphere is changing,
• the extent to which observed changes are the consequence of human activity, such as the emission of carbon dioxide and other greenhouse gases, or of natural variations driven by, for example, the Sun or volcanoes,
• why Earth’s surface warmed barely, if at all, in the last decade,
• why the atmosphere just 20 km above the surface is cooling instead of warming,
• how Earth’s temperature might evolve in the 21st century,
• when — and whether — the ozone layer will recover from its two-decade decline due to chlorofluorocarbon depletion…

Introduction

Climate, or the average of day-to-day weather, can be very different at various points on Earth. The local climate in the Arabian Desert is hot and dry, while that in the Amazon River basin is hot and humid with frequent rain. In upstate New York, the climate changes from being warm in the summer with sporadic rain to cold in the winter with sporadic snow. Hawaii, on the other hand, has a pleasant climate all year long. However, the day-to- day weather at all of these locations is much more variable. There can be dry days in the Amazon jungle, and rainy days in the Arabian Desert. There are some days in winter that are warmer than some days in summer. For further contrast, daylight in Antarctica lasts up to six months at a time with freezing cold day-in day-out. Can a climate model be built that can reproduce all of this complex behavior?

Key Points

Most basic are the near-daily measurements of surface air temperature at meteorological stations around the globe, some dating back to the 18th century. There are also precise measurements of the key atmospheric greenhouse gases (CO₂, CH₄, N₂O, O₃, CFCs) that are associated with fossil fuel burning and with other human industrial activities. Accurate monitoring of changes in solar irradiance and other radiative forcings that impact the climate system is likewise important. But these latter effects are small compared to the anthropogenic greenhouse gas forcings. The other important components of the scientific documentation of global climate change include field campaigns, theoretical studies, and laboratory analysis of climate-constituent radiative properties…

Introduction

David Rind has played a central role in the science of the modeling of climate change. He was the scientific driving force behind the development and evaluation of the first Goddard Institute for Space Studies (GISS) global climate model (GCM), ‘Model II’ (Hansen et al., 1983). Model II was one of the three original GCMs whose projections of climate change in response to a doubling of CO₂ concentration were the basis for the influential Charney Report that produced the first assessment of global climate sensitivity. David used Model II to pioneer the scientific field of climate dynamics, performing a broad range of investigations of processes controlling individual elements of the general circulation and how they changed over a wide range of past and potential future climates (e.g., Rind and Rossow, 1984; Rind, 1986, 1987). The defining characteristic of David’s papers is his unique talent for tracking down the myriad links and causal chains among different parts of the nonlinear climate system. Rather than viewing climate using a simple forcing-and-response paradigm, David showed that the global energy, water, and even momentum cycles are coupled via the general circulation and its transports…

Storms, Storm Tracks, and Expected Changes with Global Warming

Extratropical cyclones are the familiar low-pressure systems that dominate day-to-day weather over much of the planet. These storms follow typical paths denoted as storm tracks. They are important weather makers, bringing rain, snow, and sometimes damaging winds, and they are the engines of the mid-latitude climate system, carrying heat, moisture, and momentum from the subtropics towards the poles. Rainfall in mid-latitudes concentrates along the storm tracks. How these storms will change with a changing climate is, therefore, a leading question for how the weather and climate will be different on a warmer Earth…

Introduction

Climate change and its impacts is one of the most important challenges facing our society. Throughout his career, David Rind has been a pioneer on this topic, publishing many papers on the topic of climate change from past climates, most notably ice ages to future climates with much greater greenhouse gas (GHG) concentrations than found presently in the Earth’s atmosphere. For example, David Rind’s seminal paper ‘The Dynamics of Warm and Cold Climates’ (Rind, 1986) explored the zonal mean properties of the Earth’s atmosphere under a range of past, present, and future cold and warm climates. Here, I present a short lecture on climate change, specifically how Arctic amplification (AA) might influence extreme weather in the mid-latitudes. David Rind did publish on polar amplification (e.g., ‘The Consequences of not Knowing Low- and High-Latitude Climate Sensitivity’, Rind, 2008) but not as it pertains to extreme weather; a topic that is still emerging. Still, I know that David is sensitive to our limitations to understand the climate and appreciates unexpected and mysterious twists and turns in the climate system.

Introduction

Over the last several decades, we have seen a rapid evolution in both global reanalysis datasets and climate models. In the 1970s and 1980s, models existed only with coarse spatial and temporal evolution. For example, when I first came to NASA GISS to work as a programmer, the GISS model was run on an 8° × 10° (Lat/Lon) grid, with output produced monthly. By the time I received my Ph.D. in 2000, the GISS GCM was being run on a 2° × 2.5° (Lat/Lon) grid, with daily output available. During my time at GISS (December 1987 to June 2001), the separation between climate and weather was quite clear. There were weather models (e.g. Nested Grid Model (NGM) and Global Forecast System (GFS)) and there were climate models. While weather models could be run at a higher resolution, the amount of computer power needed to run for more than a week real-time prevented their adaptation to climate problems. Appropriate climate model applications included only the most general aspects of the Atmospheric Circulation. Another limitation was that the older GISS model (and GCMs in general) was run with climatological sea-surface temperatures (SSTs) and later, with observed SSTs; the latter allowed for some rudimentary assessment of impacts of El Niño Southern Oscillation on the general circulation…

Introduction

David Rind’s legacy is not only that he did great science, that he is an intellectual mentor for an impressive number of very successful scientists, but that he is an inspirational role model of how to be scientist. He grew up in the shadow of Yankee Stadium, and being a devoted Yankees fan, I believe that he first observed an atmospheric breaking wave over those hallow grounds. I always wondered if this vision over Yankee Stadium inspired him to be such a preeminent atmospheric scientist. Before spending some time discussing some of his research examining how changes in climate could impact water resources, I first want to present what I will call David Rind’s Words of Wisdom (at least as I remember): (1) ‘Hit it with a sledge hammer’, (2) ‘Nobody complains when they get an “A”’, (3) ‘No one looks very smart when you argue with an idiot’, and (4) ‘I would pay someone to clean out my desk’.

Soil Moisture — Atmosphere Feedback

The moisture held within the top meter or two of soil is a very tiny fraction (less than 0.01%) of the Earth’s total water (Eagleson, 1970). Nevertheless, its presence at the interface of the land and atmosphere gives it inordinate importance in the context of climate variability. Simply put, soil moisture variations can help determine meteorological variations. Consider, for example, an anomalously high evapotranspiration rate induced by a high soil moisture content. The high evapotranspiration can lead to an anomalously cooled land surface and thus cooler air temperatures (Seneviratne et al., 2010), and it can also lead to modifications in the evolution of the boundary layer, with concomitant impacts on the generation of convective rainfall (Betts et al., 1994)…

The Definition of Drought

The Intergovernmental Panel on Climate Change (IPCC) reported widespread agreement among climate model projections on emerging patterns in the global hydrologic cycle in the 21st century, such as increased precipitation at high latitudes, decreased precipitation in the subtropics, and increases in the frequency of heavy precipitation events, all of which would lead to permanent changes in annual and seasonal runoff and groundwater recharge (IPCC, 2007, 2013). These changes in the hydrologic cycle could fundamentally alter the nature of drought and flooding in many regions. In areas that are currently using a large proportion of their available water resources, these changes could prove challenging…

Introduction

Lightning is one of nature’s most beautiful and awesome sights. Yet it can also be extremely dangerous, presenting a major natural hazard in many different environments, from power utility companies, to civil aviation, to golfers, and more. Thousands of people are killed every year by lightning bolts, while tens of thousands are injured as well (Cooray, Cooray and Andrews, 2007). Lightning impacts both our daily commercial and recreational activities. In the United States alone, damages due to lightning strikes amounts to tens of millions of dollars annually (Curran, Holle and Lopez, 2000). In recent years, with great interest in renewable energy, wind turbines have become extremely vulnerable to lightning damage (Glushakow, 2007). Furthermore, most commercial airliners are struck about once a year by lightning; however, due to the protective metal skin, generally little damage is incurred. Tens of thousands of fires are also ignited by lightning every year, generally in temperate or high latitudes (e.g. Canada, Siberia, etc.) (Stocks et al., 2002). In such cases, tens of fires can be ignited locally on the same day as a storm passes through, causing major problems for fire crews and fire management. Hence, knowledge of how lightning activity may change as the Earth’s temperature changes is of critical importance and interest…

Introduction

Sea ice is a crucial component of the climate system in both polar regions, reflecting solar radiation back to space, hindering exchanges of heat, mass, and momentum between ocean and atmosphere, and having numerous other impacts both on climate and on polar ecosystems. In view of these impacts and the interconnectedness of the global climate system as a whole, David Rind early on recognized the potential importance of sea ice changes to latitudes far equatorward of where the sea ice is and led a study to quantify those changes (described below)…

Introduction

Sea ice is an important component of the global climate system. Sea ice forms, grows, and melts in the ocean. Sea ice grows during the fall and winter and melts during the spring and summer. Sea ice can melt completely in summer or survive multiple years. Sea ice can be classified by stages of development (thickness and age), that is, first-year sea ice (ice thickness typically <1.8 m) and multiyear sea ice (ice thickness typically >1.8 m). Sea ice occurs in both hemispheres. In the Northern Hemisphere, sea ice develops in the Arctic Ocean and surrounding bodies including Hudson and Baffin Bay, Gulf of St. Lawrence, the Greenland Sea, the Bering Sea, and the Sea of Okhotsk (sea ice can be observed as far south as Bohai Bay, China, ∼38°N). In the Southern Hemisphere, sea ice only develops around Antarctica, reaching a maximum equatorward extension at around ∼55°S)…

Introduction

Currently, there is considerable focus on the inexplicable increasing trend in time of the average Antarctic sea ice extent (Parkinson and Cavalieri, 2012), often noted in the context of the rapidly decreasing Arctic sea ice cover. While the increasing Antarctic sea ice trend was originally considered small, Simmonds (2015) has recently shown that it cannot be considered small anymore. Unfortunately, the social media uses this Arctic–Antarctic comparison in an attempt to further emphasize the paradox of the increasing Antarctic sea ice cover (often to emphasize the failings of global warming ‘alarmists’), but such a comparison is unwarranted. The differences are so dramatic between the two poles that one is not justified in expecting the change in the Antarctic sea ice to echo that of the Arctic. For example, consider the geographic setting: the Arctic is a land-locked ocean that constrains the ice, whereas the Antarctic is a continent surrounded by ocean with primary winds blowing the ice floes to warmer waters where they rapidly melt. As a consequence, the Arctic until recently was largely covered by a relatively thick (∼3 m) perennial sea ice cover, whereas the Antarctic polar oceans are covered by a large thin (∼0.6 m) seasonal ice cover, with only small areas of perennial ice. Loss of Arctic highly reflective perennial ice in summer exposes the dark absorbing Arctic Ocean waters, driving the ice-albedo feedback and greatly enhancing the absorption of heat and enhanced melt back. In the Antarctic, the thin sea ice melts in spring, so the summer ocean water is always exposed, greatly limiting the ice-albedo feedback potential. But, even given these differences, we would still expect the Antarctic sea ice fields to decrease given a warming Earth…

Introduction

The last glacial maximum (LGM) at approximately 23–18k (k—thousand calendar years) provides an important contrast to our present and pre-industrial climate in a warming world. Global observational datasets of LGM land and sea surface conditions have been synthesized and present some interesting challenges both for providing another scenario for understanding climate change and for climate sensitivity. These challenges are ongoing, as data increase and modeling improves. By definition, the LGM is defined as the time during the last glacial interval in which maximum ice was sequestered in ice sheets as visible in the marine isotopic records. Maximum cooling is visible from pollen and macrofossil records ¹⁴C dated to this interval, and ice sheets and alpine glaciers are roughly at their maximum extent throughout the globe. The ice cores extracted from Greenland and Antarctica have given us high-resolution records of greenhouse gases, dust, and isotopes of hydrogen and oxygen which reveal the progression out of the LGM at 18k as climate warmed…

Rising Seas and Coastal Hazards

Our planet is heating up largely because of increasing anthropogenic greenhouse gases from fossil fuel combustion and deforestation. Atmospheric levels of carbon dioxide and methane are now the highest in 800,000 years (Brook, 2008). Mean global temperature has increased by 0.7°C during the 20th century, likely surpassing temperatures of the past 1000 years (IPCC, 2013; Marcott et al., 2013)…

We have learned from our brilliant and dedicated colleague, David Rind, that the already-evident and further-anticipated process of anthropogenic climate change raises worldwide concerns regarding agricultural production, food security, and public health. The four pillars of food security — its availability, accessibility, utilization, and stability — will all be affected by the expected changes in climate over the coming century. At both global and regional scales, the Intergovernmental Panel on Climate Change (IPCC) has demonstrated that the provision of food security and maintenance of ecosystem services are under threat from dangerous human interference in the Earth’s climate (Porter et al., 2014). The FAO emphasizes that the main cause of hunger and malnutrition is not the lack of food per se, but the inability of vulnerable groups to access food in many circumstances (FAO, 2014). Furthermore, the IPCC has determined that global food prices will likely increase by the year 2050 as a result of changes in temperature and precipitation (Porter et al., 2014; Nelson et al., 2014). At country scales, nations are concerned over potential damages that may arise in coming decades from climate change impacts on agriculture and the food system, as these are likely to affect their citizens’ well-being, regional planning, resource use, trading patterns, and international policies…

Introduction

Tropospheric ozone and aerosols affect climate on both regional and hemispheric scales (Fiore et al., 2012, Unger, 2012). Climate change, in turn, influences the distribution and lifetimes of these species, with consequences for human health and ecosystems (Jacob and Winner, 2009). Understanding the coupling between short-lived chemical species and climate change is a major challenge, given the uncertainties in chemical mechanisms and climate processes. For example, aerosols perturb regional climate directly, through absorption and scattering of incoming sunlight, and indirectly, through interactions with cloud droplets. Neither the optical properties of the mix of aerosols in the atmosphere nor the details of cloud-aerosol interactions have been wellcharacterized (Rosenfeld et al., 2014; Chen et al., 2015)…

Introduction

Climate change will profoundly impact Earth’s environmental health as well as the world’s economic and geopolitical landscape over the coming decades. The impacts of climate change are, in fact, already beginning to be experienced and have the potential to affect every living plant and animal on Earth within decades (IPCC, 2014). Given this reality, every citizen of this planet should have the right to knowledge about the Earth’s climate system and have the option to adapt to, or help mitigate the profound changes that are coming. In addition, a portion of the workforce needs to be capable of interpreting and analyzing climate information because, since the impacts of climate change will be widespread, pervasive, and continue to change over time, more professions will be interacting with climate data. We are already at, or past, the point where educators and their students require access to the scientific and technological resources — computer models, data, and visualization tools — that scientists use daily in the study of climate change…

The following sections are included:

• About the Editors
• Appendix — Supplementary Material