Typically, we talk about positive feedback loops (self-reinforcing) and negative feedback looks (where the current direction of change is discouraged). Our example with the furnace is a negative feedback loop in both directions. Move towards too hot, and heating is stopped. Move towards too cold, and heating is applied. If you want stability, you want negative feedback loops.

Catastrophic Climate Change (CCC) is effectively a suicide pact by the entire human race. We will not give up our profligate use of fossil carbon fuels, the burning of those fuels is driving climate change, and climate change is now killing us.

Greenhouse Effect

It's been explained so many times I'm tempted to skip it. But here it is in feedback loop form. The more greenhouse gases (e.g., carbon dioxide, methane, water vapour) there are in the atmosphere, the more the planet warms (visible light reaches the planet surface, much of which is converted to infra-red (heat) energy, and that has a harder time escaping from the atmosphere, and the planet warms as a result. However, as the planet warms, it creates more water vapour in the atmosphere (warm air can carry more moisture), increasing the greenhouse effect. As the planet warms, there are more forest fires and crop failures, creating more carbon dioxide, increasing the greenhouse effect. As the planet warms, more life in oceans, fresh water and swamps die, decomposing anaerobically, creating more methane, increasing the greenhouse effect. As the greenhouse effect raises temperatures, the cycle continues to spiral with more intensity until the planet is no longer suitable for human habitation.

Carbon Dioxide

In general, as plants grow, they absorb (net) carbon dioxide from the atmosphere or water where they live. When they die in an oxygen-based surrounding, they release that carbon dioxide (greenhouse gas) back into the atmosphere. When more plants die due to fire (intentional or not), that carbon dioxide is released very quickly. When those plants decompose slowly (treefalls in forests, killed by drought or harvesting), the carbon dioxide is released more slowly - but it is still released - which means more greenhouse gas and greenhouse effect, which leads to more dead plants ....

Methane

Remember, the global warming potential of methane is 56 times that of CO2 based on a 20-year timeframe. We can no longer work in terms of 100 year time frames. Climate change is no longer offering us that much time. We have to change this part of the conversation NOW! As more methane (e.g. fugitive leaks from the gas industry) enters the atmosphere, the more planetary warming it forces. As the planet warms, more methane is released into the atmosphere from various sources, like permafrost melt, clathrates, increased breaks in gas pipelines related to extreme weather and 'natural' disaster events. Those are positive feedback loops.

May 2019 - The Methane Detectives: On the Trail of a Global Warming Mystery

There may be more sources of methane we are not accounting for, as measured amounts are rising faster than expected.

Methane being released faster than ever, posing new threat to Paris climate goals (The Independent)

Did you know that floating plastic pollution is a cause of methane and other GHG emisisons? Greenhouse gases linked to degrading plastic

Unfortunately, our feckless elected leaders are not prepared to deal with plastic pollution, because it is not profitable. Perhaps that's because we massively subsidize the petrochemical industry worldwide so that new plastic is cheaper than recycled plastic.

If you are interested in the potential of reducing the amount of microplastics pollution in our wild waters, check out RESTCo on capturing microplastics.

Permafrost Melt

February 2019 - Defusing the methane bomb—we can still make a difference (Phys.Org)

August 2018 - 'Abrupt thaw' of permafrost beneath lakes could significantly affect climate change models (Phys.Org)

February 2019 - What is permafrost and why might it be the climate change time bomb? (South China Morning Post)

Methane Clathrates

(aka 'fire-ice', hydromethane, methane hydrate and other names)
The key issue with methane clathrates is that they are large stores of 'frozen' methane, which are thawing and leading to large releases of the potent GHG. As the world warms, more melting clathrates; with more methane in the atmosphere, the more the world warms. Classic positive feedback loop.

Nitrous Oxide (N2O))

Nitrogen oxides are produced by internal combustion engines (oxygen and nitrogen taken from the air are combined in a heat reaction - we call these engines 'heat engines' for a reason). Nitrogen oxides are a smog precursor and a potent GHG in their own right GWP: 310 times that of CO2 on 100 year duration.

Atmospheric Water Vapour

Yes, water vapour in the atmosphere predates the human industrial age. But so do carbon dioxide and methane in the atmosphere. And yes, human activities are increasing the amount of water vapour in the atmosphere.

The Rest

There are other greenhouse gases, but my understanding is that their total contribution to the problem so far constitutes less than a rounding error compared to any of the big for (carbon dioxide, methane, nitrogen-oxides, and water vapour).

Forest Fires

Forest fires are getting worse as the planet warms and wooded areas dry out in the summer. Forest fires create carbon dioxide, soot and heat from burning the trees and brush. The carbon dioxide is a greenhouse gas, so it heats the planet even more (positive feedback). The heat from the flames adds directly to climate change warming effects, causing more warming (positive feedback). The soot lands and darkens the surfaces it lands on, especially Arctic glaciers. The darker surface turns more solar energy into heat, melting the glaciers, adding to sea level rise and adding to planetary warming (positive feedback).

February 2019 - Canada's forests actually emit more carbon than they absorb — despite what you've heard on Facebook (CBC)

Albedo Effect

What's an 'albedo effect'? In short, it is the measure of how much an object reflects sunlight and avoids turning it into heat. As you undoubtedly know, black (matte) surfaces get hotter in the sun than high gloss white surfaces. The more visible light a surface reflects (like fresh snow), the less heat it produces on its surface, and the cooler it feels to our touch. The higher the reflectivity, the higher the albedo value. There's a bit more to it than just the monochomatic shade of a surface's colour. Shiny surfaces reflect more light than matte surfaces. Tree leaves tend to be more reflective than their monochromatic shade value would suggest.

As we continue development in the business as usual scenario, we are darkening the planet, which leads to a lower overall albedo number and more warming. A dark roof of asphalt shingles absorbs more energy than the open field or forest it displaced. Burning trees to open land for agriculture drops the albedo of that zone, while also adding carbon dioxide and soot to the atmosphere. Same for uncontrolled forest fires. The soot darkens the area it lands on, negatively affecting albedo. The loss of glaciers and Arctic sea ice to warming also increases heat absorption by lowering albedo. Another positive feedback loop / death spiral - a darker planet (lower albedo / light energy reflection) warms more; a warming planet leads to darkening and lower albedo.

Waste Heat

The core problem with climate change is that the planet is getting hotter, to the point humans may not survive the current path. Adding more heat seems a poor strategy, yet that is what we are doing on multiple fronts.

Nuclear fission electricity generation creates massive amounts of waste heat, which is why most nuclear plants are put beside large bodies of water, to provide cooling. A nuclear fission plant is typically about 30% efficient (electricity produced vs. heat energy to make steam), not counting the energy used to mine and refine uranium, build fuel bundles, store spent fuel, build the actual plant, decommission the plant, and permanently dispose of the spent fuel and other high-level radioactive waste.

Coal-fired generation is about 30% efficient as well, not counting the energy spent to mine, process, clean and transport the coal to the plant. This also makes no allowances for disposal of fly ash or materials captured by scrubbers or released from the smokestack.

Natural-gas generation is typically between 35% (low-cost peaker plants and old plants) and 45% (combined cycle technology). Again, this does not include the energy consumed to produce and transport the natural gas to the plant, or deal with any of the smokestack emissions.

Light duty vehicles (cars and small trucks) typically have real-world efficencies well below 20% (e.g. idling efficiency is 0%, engines are less efficient when cold which is the majority of urban commute driving). Most of the conversion losses are expressed as waste heat, and a small amount as noise (vibration).

As we keep adding those heat sources to the planet's atmosphere, this leads to more warming, and adds to the other feedback loops accelerating climate change.

Algae Blooms

A bit of algae (specifically microalgae) in wild waters tends to be a good thing for the marine life food chain. The problem is when there is too much algae. How much is too much? Pretty much if you can see it forming on the water surface, that's too much. Algae blooms are growing in size, duration and where they occur. Algae flourishes (to bloom levels) if they have 3 things: warm water, nutrients (notably nitrogen and phosphorus), and they prefer calm waters. Humans are supplying all three. The warming of the planet's surface is warming surface waters. Industrial farming in particular is providing large quantities of nitrogen and phosphorous via fertilizers and livestock feces, which is washed off farmland and pastures with rain and springtime snow melts. Aquaculture, breakwaters, wharves, docks, and shrinking inland water bodies are reducing wave action and currents, making for calmer (and warmer) water. Thus, algae blooms are bigger, showing up in new places and last longer than a couple of decades ago. That's bad enough. But it gets worse.

When algae dies off as colder weather arrives, or simply because it has exhausted the available nutrients, it becomes heavier than water and sinks to the water bottom. Having died, it decomposes. Because it is under water - and particularly in oxygen depleted water due to the algae itself - it produces methane when it decomposes. Methane is a greenhouse gas - 56 times as potent as carbon dioxide in terms of global warming potential. So, think of it like this: algae consumes carbon dioxide as it grows, but it releases methane when it dies - a factor of 56 multiplier in terms of climate change impact. Now, THAT's a feedback loop!

But there's more. When the algae dies, it releases the nutrients it used to grow, the nitrogen and phosphorus, to sit on the water bottom over the winter. But the following summer, as the water warms and the algae starts to grow again, that nutrient inventory is available to feed the new crop of algae - aided by the fresh nutrients in this year's run-off. That's not just a feedback loop, that's pouring fuel on a fire!

Finally, as waters warm further, the types of algae which grow tend to shift away from green phytoplankton microalgae (which is cosmetically unattractive and kills marine life in the water column by removing oxygen and reducing sunlight penetration into the water) to cyanobacteria (or 'blue-green algae') or even alexandrium fundyense, alexandrium catenella or karenia brevis ('red tides'). The latter two contain toxins (even neurotoxins) which can be harmful to humans and other animals, including fish and shellfish.

Coral-Algal Phase Shifts

Climate Change Induced Coral Bleaching and Algal Phase Shift in Reefs of the Gulf of Mannar, India (June 2013)