Looking through the weekly discussion threads, I notice that very little energy has been devoted to discussing the hints the show is giving about the situation on Earth. Maybe its because they have all been dropped as parts of scenes where other stuff is going on, but after the mass graves line this episode I went back to collect all the references I could find and holy shit is it worse than I think most of this sub realizes.

Area of Direct Effect

This can all be fairly well illustrated by the journey we see Amos and Clarissa take. Note that the prison they escape from was in "Chesapeake", which could be approximately in Southeastern Virginia. The North American rock hit nearish Philadelphia based on comments we've heard about the locations of relief centers and affected areas. That's a straight-line distance of about 270 miles or 438 kilometers from Chesapeake, VA, and yet the whole prison was wiped away? This is the first piece of evidence we see that should tell us we're not dealing with a small nuke level impact here.

Tsunamis

In Avasarala's office we see that flooding from the strikes (probably the ocean hit in Africa) has broken the sea walls in NYC and flooded the city. We hear from the new SG that he saw towers collapsing as he escaped the city. When Amos and Clarissa are biking towards Baltimore we see waterlogged ground. We hear from Erich about how the city is underwater, with whole neighborhoods washed away by the waves. In short, up and down the coast the cities are having straight up bad days.

In the modern world, about 40% of the global population lives on the coast, a percentage that is just expected to increase as urban centers continue to draw more population. Given the ocean hits in Africa and SE Asia, we can assume a good portion of that significant population is feeling the direct effects of the Rocks' tsunamis.

In other words, just around half of the global population is living in urban centers with out of commission electric, food, water, and transportation infrastructure.

Nuclear Winter

This will be a pretty short section because the idea of a nuclear winter is well-established in the collective cultural context. Remember that scene where Peaches is going on about the Moon and Amos offhandedly comments he's pretty sure that's the Sun? Yikes.

Another piece of evidence in favor of this is the actors' attire throughout the season. When Amos arrives in Baltimore everyone is wearing lightly-cold gear. From living in the general vicinity, I can tell you that's what people wear when its chilly but not cold, maybe in 55-65 Fahrenheit (12 to 18 Celsius) range. The full winter gear you see people in when Amos and Peaches arrive in Baltimore after the Rocks, though, is what people are in when its more like 20-30 (-6 to -1).

That plus the omnipresent snow as they journey towards New Hampshire is not a promising sign for the prospects of a quick recovery.

Food, Water, and Electricity

Consider this - would we, today, realistically have the ability to repair half of the global infrastructure quickly enough to prevent significant disaster? Even with our much more fully educated and employed population? Even assuming the other 50% of the world was unaffected by whatever disaster caused this? Short answer: no.

Meanwhile The Expanse's Earth is heavily overpopulated with an economy almost certainly as, if not more, reliant on the transportation of goods across continent- and ocean-wide distances as we are today. What's more, all of that transportation almost certainly relies on electricity. Each bit of infrastructure we've seen suggests this. Electric trains in Baltimore, electric bikes, and hell even using batteries for teakettle takeoffs. So our transportation infrastructure is electric - all good, lets just plug in batteries!

The problem is that you almost certainly lost a good amount of the power generation capability of Earth in the initial strikes and tsunamis. After all, power generation infrastructure tends to be collected near the population centers they serve, and we already established that around half the Earth’s population is in the possible area of tsunami effect. Then add in the problems with solar panels due to a global nuclear winter and things are not looking great for electricity generation on Earth.

No biggie, right? We can just use the power from the other stations to go in and fix it all! Nope. Notice the show's multiple explicit mentions about places continuing to lose power and communication: even places like Montana! Remember the cascade on Ganymede? On an already heavily-loaded infrastructure, around half of it just went dark. The more load the rest of the system gets, the more likely are the problems on certain branches, and the more stress the rest of the system gets.

So even in unaffected areas our power infrastructure is starting to crap out, and that's having the knock-on effect of taking down the global transportation infrastructure. In turn, this is making it harder to maintain even the un-hit infrastructure, not to mention get supplies to the areas in need. Sure we can use batteries for a while, but as the grid continues to collapse where do you propose we charge them? Emergency solar panels? The clouds and dust causing the nuclear winter merc'd those, sorry.

Even today, grocery stores are only ever a couple resupply trucks away from running dry. With power and thereby transportation infrastructure failing, supplies in these massive cities are going to start running out quickly.

So even if you can get your tractor running on emergency power, even if you can get that to a factory or processing plant, even if that plant also has emergency power, even if you can find a truck to transport that food to a store, you've helped relieve the stress for a couple days maybe. Just enough time for more paths in the complex global supply chain to fail and make the task even harder next time.

You'll note here Erich's gang in Baltimore clearly hoarding and guarding a massive nest of supplies and the comments from the staff on that island in New Hampshire about food running out and power and communication being out for days.

One extra point noted by /u/OrionAstronaut is that we hear comments about desalination plants failing. The need for them in the first place suggests general clean water shortages, which are unlikely to get better given all the problems listed above.

Mass Graves

We now return to the comment that started me off on this search - the mass graves on the road between Baltimore and New Hampshire. That should be self-evidently bad, and a sign that we're starting to see the effects of a global collapse in the infrastructure that keeps billions of people alive in addition to the direct effects of the Rocks themselves. Another poignant on-screen example of this is the old folks' home with the body bags. That's not a good sign for the security of the global infrastructure.

Why doesn't the UN seem to care?

Naturally all of this leads to why isn't anyone high up putting this together? Well, we've gotten hints. Think of the comment in the Cabinet meeting about how "relief centers have experienced a significant surge in uptake" and subsequently "things are getting bad down there." Keep in mind, though, that this group of people is also trying to deal with a system-wide conflict and grew up in a world where asteroids haven't been a real threat for generations, and where communication, power, and the ability to easily get into space have been basic components of the human experience for centuries. In short, they aren't seeing it in person, the people experiencing it in person probably don't have the electricity or connection to show just how bad it is, and they're distracted. This is a UN that has run tens of thousands of disaster relief campaigns during its history. All of them have gone well, so why should this time be much different? Plus, its probably been a few weeks at best since the Rocks hit.

In short, this is somewhat of an out of context problem for them, they're insulated from just how bad it is, and they're distracted. I suspect we'll start to see a recognition of just how bad things are getting in the finale or as we dive into Season 6.

Note

This doesn't even get into the effects of the (presumably) main source of live soil and food for most of humanity getting effectively ripped out of the solar supply chain. Past the Earth's atmosphere, humanity lives in another simple-complex system, like Ganymede but bigger.

tl;dr

• The directly affected area is way too big to be just a little nuke level impact
• The indirect impacts from things like tsunamis have screwed up at least 50% of the world's population, power generation, transportation, and communication infrastructure
• We see clear evidence of a nuclear winter which is not helping the situation.
• All of this combines to cause a cascade that will effectively cripple the global infrastructure and cause starvation, freezing, death, etc.
• We see and hear direct on-screen evidence that this is happening.

tl;dr ELI5 Earth is fucked. We keep hearing about how "millions" died but its shaping up to be a whole lot more.