Minnesota Mathematics of Climate Seminar
September 3, 2024
An Introduction to Earth's Heat Imbalance, Richard McGehee, School of Mathematics
The changes in Earth's climate that have occurred during the last half century are a result of simple physics: there is more solar energy absorbed by Earth than is reradiated back into space. In this introductory lecture we will examine the scientific evidence for this imbalance, show the data estimating the magnitude of the imbalance, and extrapolate the data into the future. We will also examine the role of atmospheric carbon in creating the imbalance.
September 10, 2024
An Introduction to Budyko's Energy Balance Model , Richard McGehee, School of Mathematics
In 1969 Budyko proposed an energy balance model to explain the existence of Earth's ice caps. The components of the model include incoming solar radiation, outgoing long wave radiation, albedo, and redistribution of heat across latitudes. The model can be used to show how the ice caps change with a changing climate and to examine the possibility of a snowball Earth.
September 17, 2024
Budyko's Model and Snowball Earth, Richard McGehee, School of Mathematics
Budyko's energy balance model can be used to illustrate how a Snowball Earth could form and how it could end in a rapid melt to an ice free Earth.
September 24, 2024
Forests and climate change, Lee Frelich, Department of Forest Resources, University of Minnesota
Minnesota is at the confluence of three biomes: boreal forest, temperate forest and grassland. With major climate-sensitive ecotones between these biomes crossing the state, and with a location in the center of the continent where temperatures are expected to increase more than the global average, Minnesota is a great laboratory for studying the impacts of climate change on forests. Depending on low or high greenhouse gas emissions scenarios, alternative futures include biomes moving northeastward a short distance, so that Minnesota would not look much different than it does now, or much longer distances, making Minnesota a prairie state more like Kansas. In the latter case, the boreal biome could vacate the state, along with a number of northwoods tree species like red pine, jack pine, white and black spruce, and paper birch Furthermore, a number of other factors are likely to exacerbate these impacts and push change faster than if it was responding to increasing temperature alone. These include more droughts, more frequent and larger fires, more compound disturbances (e.g. windstorms followed by fire), insect infestations and phenological changes (e.g. earlier springs). We will explore models used to project future changes in forests to a warming climate and associated changes in the environment, and discuss potential future scenarios.
October 8, 2024
Welander's Ocean Circulation Model, Richard McGehee, School of Mathematics
The Hollywood movie The Day After Tomorrow portrayed the Earth falling into a new ice age as a result of a weakening gulf stream caused by global warming. Although counterintuitive, such a phenomenon occurred during the last glacial retreat. A simple model of ocean circulation introduced in 1982 by Pierre Welandar illustrates this phenomenon. The model lends itself to analysis using mathematical techniques only recently developed.
October 15, 2024
Insights into how Earth accumulates heat: Manifestations of radiative forcing and feedback in the satellite record, Shiv Priyam Raghuraman, Department of Climate, Meteorology & Atmospheric Sciences, University of Illinois
How Earth gains and loses energy is key to its habitability because perturbations to the planetary radiation balance alters the entire climate system. We now not only have continuous satellite observations of Earth's radiation budget, but also climate models that represent the Earth system better than ever before. My talk will focus on understanding why Earth is accumulating heat rapidly by leveraging satellite observations and climate models. I will demonstrate how anthropogenic radiative forcing and feedbacks from greenhouse gases, aerosols, clouds, and sea-ice changes have caused an increase in Earth’s energy imbalance.
November 12, 2024
An Introduction to Multiflows, Richard McGehee, School of Mathematics, University of Minnesota
Early in the 20th century Hadamard introduced the concept of a well-posed problem as a model for which (1) solutions exist, (2) solutions are unique, and (3) solutions depend continuously on initial conditions. Although solutions are not unique in Welander's box model of ocean circulation, the model is useful in understanding oscillations in ocean circulation. Welander's model is an example of a general class of models called Filippov systems. In this lecture we discuss a further abstraction, called multiflows, which provide a framework for proving general theorems about models where the insistence on uniqueness is relaxed.
November 19, 2024
Exoplanets in 1D and 2D: from ice cover to atmospheric circulation, Ekaterina (Kath) Landgren, Visiting Fellow, Cooperative Institute for Research In Environmental Sciences, University of Colorado, Boulder
The diversity of planetary environments in our galaxy provides a rich laboratory to explore atmospheric and climate dynamics across different regimes. We first explore stable ice configurations on terrestrial planets using two energy balance models with explicit obliquity dependence. Our analysis shows that partial ice cover is possible for any obliquity, with snowball transitions influenced by albedo contrast and heat transport. These results inform the climate stability of rapidly rotating planets in habitable zones. We then investigate the atmospheres of synchronously rotating sub-Neptune type exoplanets using our open-source model, SWAMPE (Shallow-Water Atmospheric Model in Python for Exoplanets). Simulations reveal how radiative timescales and rotation rates shape temperature contrasts, variability, and circulation regimes. In highly irradiated, short-timescale regimes, the simulations exhibit high day-night temperature contrasts. As the timescales become longer, the temperature contrasts and longitudinal variability decrease, while temporal variability increases. This work provides insights which can help constrain and make predictions for observations.
November 21, 2024
Why does the U.S. public underestimate climate policy support?, Ekaterina (Kath) Landgren, Visiting Fellow, Cooperative Institute for Research In Environmental Sciences, University of Colorado, Boulder
Despite climate change being a polarizing issue in the United States, many climate change mitigation policies enjoy the support of large public majorities. However, a recent study found that most Americans underestimate public support for climate policies, often by 20 points or more. The implications of such widespread misperception range from individual behaviors to legislative outcomes. Here, we combine theory and empirics to explore two possible explanations of climate policy misperception. Homophily---the tendency of like-minded individuals to selectively associate with one another---could isolate opponents of climate policy from countervailing majority opinion. False balance in media---over-representation of negative opinions about climate policy---could exaggerate public perceptions of their prevalence. We use an agent-based social-network model of opinion and opinion perception to predict the severity of homophily and false media balance needed to explain observed misperception of climate policy support. Our model suggests that homophily alone cannot explain observed misperception, but homophily combined with false media balance could explain it. We then analyze discussions of climate change in 2,072 recent news transcripts from major media outlets. We find that climate policy is largely omitted from news coverage of climate change, and discussions of climate policy are polarized across news networks. However, we do not find evidence of false balance---over-representation of negative opinions of climate policy compared to public opinion---across the networks, on average. We discuss alternate hypotheses, which might better explain misperception of climate policy support, for future research.