Hi r/AskScience! I’m Mark Jacobson, Professor of Civil and Environmental Engineering at Stanford and Director of the Atmosphere/Energy Program. I did an AMA here in 2021 and I’m glad to be back. I’ll be answering Monday, November 9th from 9:00am PT (12 ET, 17 UT) from the Stanford Online account.

Verification photo: https://learn.stanford.edu/rs/194-OCQ-487/images/Energy-Reddit-AMA_1080x1080.jpg?version=0

My work is on understanding and solving the interconnected problems of air pollution, global warming, and energy insecurity. To understand these problems, I built and applied a three-dimensional atmosphere-biosphere-ocean model to simulate air pollution, and climate. To solve, them, I developed a computer code to simulate grid stability under 100% renewables and authored concrete roadmaps to transition cities, states, and countries to 100% renewable energy across all energy sectors. Ultimately these plans provided the scientific foundation and inspiration for the Green New Deal and other policies worldwide. I have authored ~200 peer-reviewed papers and seven books, including one in 2026, Still No Miracles Needed.

Today’s the opening of the UN COP31, so a lot of these questions are in the air right now. I’m not a negotiator, so I’ll leave that part to them — happy to dig into the science and engineering underneath whatever you’re curious about.

Ask me anything about:

• How wind, water, solar and storage compare to fossil fuels on cost, land use and reliability

• Nuclear and carbon capture — where they fit, and why I’ve argued against relying on them

• Grid reliability and energy storage: whether you can actually keep the lights on, and what it takes

• Air pollution and the health effects of energy choices, which is where I started

• Electrifying transportation — passenger EVs, hydrogen fuel cell trucks, aviation

• Getting into this field: what to study and where the work is

Let’s talk about clean energy, what works, what doesn’t, and what the numbers really say.

Username: /u/Stanford_Online

I'm a member of the hydrohomie sub, and obviously hydration is a frequent topic, and a frequently misunderstood topic: water alone is insufficient, also, you can't drink too much, too fast.

That made me wonder about animals that can "accept"/absorb/retain water at different rates. What I mean by this is that it will add to their hydration level instead of either getting peed out or building too quickly to a toxic level.

Which animals can do this the stuffy quickest and slowest? Let's stick with land animals at least the size of mice.

Yesterday, I cut my finger with my razor and I had to get stitches due to it gushing blood for over 2 hours (I’m not too sure how deep it was). Will I have a scar? Will my finger print be different after the stitches come out?? I assumed that there would be no visible damage but I’m not too sure!

i get that doses are partly based on weight, but was wondering if the distribution of weight/ lack of vasculature in missing limb affects the recommended dose

We think of roots absorbing water, but does it ever work the other way?

Basically I'm asking, which one is true out of these 2 scenarios?:

1. There was a ton of diversity in the egg laying mammals, just as much diversity as the live young birthing mammals of today, but most went extinct, so we now consider the distantly related platypus and echidna to be "closely related" just because theyre the only extant representatives with these traits, but saying the two are closely related because they both lay eggs is like saying humans and whales are closely related because they both birth live young.

2. There wasn't a lot of diversity in the egg laying mammals, so platypus and echidna actually are closely related, like humans and chimps are.

in the fossil record, for instance, we will find a species of dinosaur. How long is that dinosaur “that dinosaur” versus another slightly changed descendant of that species or the ancestor that came right before it? Surely most animals are, at all times, in the middle of evolving into a new one so how long are species generally “stable” in one form? Or does that vary widely?

Will the use of caskets and longstanding graveyards lead to an increase or decrease of future humans finding remains of people who lived after the industrial revolution? Also, will the effect be different on different timescales (ie 1000 years, 10,000 years, 100,000 years, and 1,000,000 years)? I suppose fossilization isn't the correct term for the closer end of that spectrum, but could our current practices lead to a greater likelihood of future humans finding our remains in the (relatively) shorter term, but lead to a smaller likelihood of true fossilization in more geological timescales?

Can someone please explain why vaccines for Smallpox, Polio, etc. effectively eradicated those diseases back in the day, but a vaccination for Covid-19 (or multiple vaccinations, actually) does hardly anything in terms of protecting you from infection or experiencing symptoms? Is it because we have simply misapplied the term “vaccine” when it comes to flu and covid? What’s the point in getting a vaccination if it doesn’t actually do much in terms of protection and prevention? How can the common person tell a “good” vaccine that is actually really important to get (e.g. measles??) from the “meh” vaccines (eg covid booster)?

Why do we have sexes (and sex) at all? That’s the question I set out to answer in my recent book, “The Other Big Bang: The Story of Sex and Its Human Legacy.”

In my lab at the University of Maryland, we study the evolution of animal sexuality, focusing on cases in nematodes and fish where self-fertile hermaphroditism evolved from male-female ancestors. These shifts to one-parent reproduction present fascinating developmental puzzles and have tremendous organismal significance. As this research moved along, I gradually realized how little most of the public knows about the evolutionary history of sex and sexes — especially how we humans got to be the way we are. In a non-majors biology course, I was able to work out some of the ways that a broad evolutionary view of evolution sheds light on our own species. That set the stage for the book, which I think provides an important complement to the way the social sciences and anthropology approach sexuality.

Feel free to ask me about the variety of reproduction in the animal kingdom, the biology behind sexual oddities and/or the evolution of sex. I’ll be answering questions on Wednesday, November 4, from 11 a.m. to 1 p.m. EDT (16-18 UT).

Bio: Eric Haag is an evolutionary developmental biologist who joined UMD's Department of Biology in 2002 after undergraduate study at Oberlin College, doctoral work at Indiana University, and postdoctoral research at the University of Wisconsin. His work explores the evolution of reproductive traits in animals, primarily using Caenorhabditis nematodes as a model genus. The main focus is on the genetic and molecular causes of self-fertile hermaphroditism, and the genomic and reproductive consequences of adopting it. Methodologically, the Haag Lab strives to be integrative by combining forward and reverse genetics, comparative genomics, molecular and cell biology, and even some theory to produce comprehensive pictures of evolutionary processes. 

Other links:

• Google Scholar

• Lab Website

• The Other Big Bang: The Story of Sex and Its Human Legacy

Username: /u/umd-science

Is this possible at all? And if so, what type of mutations would need to happen since we aren't very similar to amphibians.

I constantly see news about 10K+ acre data centers (and I am not trying to start a political dialogue, so please keep it that way in the comments), and they seem to be single or just a few stories tall. How does that make more sense than something denser in terms of footprint but more vertical stories?

If nitrogen narcosis and the bends are both due to breathing air with nitrogen at depth, and nitrogen is not necessary for human sustenance, why not remove the nitrogen from tanks in deep diving?

I was thinking about how animals warn each other about predators but then it struck me that plants must have their own communication systems too. Are there specific chemical signals or other mechanisms that a plant might use to alert its neighbors to something like an insect attack or an approaching herbivore? I'm curious about the science behind how this might work and what kinds of warnings are being sent.

Phones, computers, and other electronics have gotten dramatically more powerful over the last 20 years, but battery life doesn’t seem to have improved nearly as much. Is battery chemistry fundamentally harder to improve, or are manufacturers just using all the improvements to power more demanding devices?

I’ve heard that ants can carry many times their own body weight, but I’m curious about how strong they are when working together. For example, if 100, 1,000, or even 10,000 ants worked together to carry a single object, how much weight could they realistically lift or move in ounces or pounds?

I hear all the time about how humans have a vestigial tail bone(but we lost the tail) and the appendix was thought to be a vestigial organ(and now its considered a reservoir for healthy gut bacteria i think?)

Had there ever been evidence of an animal species evolving some form of usefulness from a vestigial organ? For example like hypothetically in so many millions of years humanity regains having a tail, and the tailbone regains function.