World leaders are gathering now  in Scotland at a UN summit on climate change. Their mission is to make rapid cuts in greenhouse gas emissions and limit the danger we all face from a future of more extreme heat, drought, fire, flood and hurricanes. This story is part of our commitment to tell you what it means for Texas.

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Six million Texans live close to sea level on the Gulf Coast. It's home to massive ports and one-third of the nation's oil refining. So, what does it mean for Texas when science tells us, because of climate change, the sea is rising faster now than any time in at least the last 3000 years?

What I want to know is how much do we know about sea level rise? How do we know it? And how worried should we all be? So, I’m headed to the Gulf Coast to find out.

How do we know the sea is rising?

In addition to beaches, heavy industry and vacation homes, the Texas Gulf Coast is also home to an extensive network of tide gauges that give extremely accurate sea level measurements.

Dr. Phillipe Tissot is the Interim Director of the Conrad Blucher Institute and a professor at Texas A&M Corpus Christi. He uses those gauges to study sea level rise.

“You can see sea level is rising,” Tissot tells me.

The oldest sea level records in Texas come from Galveston. Data maintained by the National Oceanic and Atmospheric Administration show, over last 100 years, sea level is up by 2 feet.

“We need to know how high the water is, and we need to know how high the water will get over the coming years,” Tissot says. "Because, if we build seawalls, if we build the other big infrastructure, those things will cost millions, hundreds of millions, even billions of dollars."

Why is the water rising?

Philippe says you've got to start with emissions from power plants and automobiles which pump huge amounts of carbon dioxide into the air. That carbon traps heat in the atmosphere - which makes the climate hotter.

Most of that heat gets absorbed by the oceans. But the heat also makes the ocean water expand, while, at same time, glaciers and ice sheets melt into the sea. The result is water that rises about the thickness of two quarters, every year, year after year.

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But Philippe is telling me, along the Texas Gulf Coast, something else is also going on, too.

The land is sinking.

“It doesn't really matter if the land is sinking or the water is rising, your feet are going to get wet either way. So, tide gauges measure the combination of both the land sinking and the water rising.”

That’s called relative sea level rise. It starts with sinking land, which is a result of pumping out underground fluids, like water or oil. That leaves a cavity below, giving the ground above room to sag.

After that, you add rising water.

Taken together, according to research from Virginia Institute of Marine Science, relative sea level rise is worse in Texas than almost anywhere else in the country.

The chemistry of ocean water is changing

So, we know the water's rising. How else is the ocean impacted by climate change?

I’m meeting up with Dr. Xinping Hu. He's an oceanographer at the Harte Research Institute at Texas A&M Corpus Christi. He’s telling me, in addition to absorbing heat from the air, ocean water is also absorbing massive amounts of carbon dioxide.

For his research, he samples ocean water, checking how much carbon dioxide is making its way into the sea.

“So, the ocean is like a CO2 sponge?” I ask him.

“Yeah, something like that,” he says. “There are people that are working on this day in, day out. And, you know, we saw this trend ever since a few decades ago when people started collecting water samples."

Dr. Hu’s telling me, adding carbon dioxide to the ocean fundamentally changes water chemistry. It makes it much more acidic.

That change interferes with how some organisms develop, like oysters, impeding their ability to make hard shells. Scientists have even discovered organisms whose shells are dissolving.

“Some species will respond, you know, in some positive ways, but a lot of it is pretty negative ways," he says. "You're running the risk of altering the balance in the ocean."

The ocean ecosystem is changing

So, we know the water is rising. And the chemistry of the water is getting more acidic. But, can you tell that things are changing?

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Katie Swanson is a Research Associate with the University of Texas Marine Science Institute in Port Aransas. She studies the impact of sea level rise on marshes, which provide essential food, refuge and habitat for fish and wildlife.

“Plants need sediment - like, they can't be in water inundated all the time,” she says.

She measures underwater sediment levels, which is basically the sand under the water that plants grow in. Her research is documenting a loss of plant life that lives in the sandy marsh.

“You're losing the marsh, and it's not being replaced anywhere else,” Swanson is telling me. “(The marshes) are just being inundated, staying in the water more frequently, which is basically drowning them."

Katie says that’s important to people, too, because marsh plants are natural protection against shoreline erosion and flooding.

“If you go to the same habitat over and over every time, we'd show up and, like, there was dry sediment in marsh plants, and now it's constantly under a foot of water,” she describes.

The fight against sea level rise

A major report, recently published by the United Nations, got the world's attention saying it's "unequivocal that human influence has warmed the atmosphere, ocean and land" – with no end to sea level rise in sight.

So, what does that mean for communities along Texas' Gulf Coast?

“What kind of responsibility do people who think about the future have to plan for this?” I ask Tissot, with the Conrad Blucher Institute, during another meeting with him.

“Folks who designed coastal infrastructure should think about it all the time,” he says.

That's what world leaders are thinking about now in Glasgow, Scotland at a UN Summit with the mission to drastically cut emissions. The goal is to limit future climate change by eliminating half of greenhouse gasses by 2030 and all of them by 2050.

Here's an example of why that matters.

Near Galveston Bay is the iconic Space Center Houston. Using research and images from the science non-profit Climate Central, the grounds are dry.

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But in a best-case scenario, a few low-lying parking lots will be consistently underwater by the end of this century and beyond - and that's if world leaders meet the challenge to limit rising temperatures.

In the worst-case scenario, if the world continues releasing emissions at the current rate, the Space Center will end up several feet underwater.

RELATED: Before and after photos show how sea level rise would inundate coastal Texas, other cities if U.S. doesn't cut carbon emissions | Interactive

Along the Gulf, in a worst-case scenario, the refineries in Texas City, the boardwalk in Galveston, and downtown Corpus Christi would be gradually swallowed by the rising sea.

“Longer term, what are we going to have either do is spend quite a bit of money to adapt or move out,” Tissot says. “Human nature has difficulty acting now to prevent something that happens in a long time. And that's really what we should be doing."

How much should we worry about this?

On this reporting trip, I learned a lot about sea level rise. The ocean is rising. We know it because scientists have been studying this for decades.

At the beginning, the big question I wanted an answer for was how much should we all be worried about this?

Watching kids play on the beach with the sun out and a breeze blowing, it doesn’t feel like there’s much to be alarmed about.

For the answer, you really have to look beyond how normal it all looks today and wrap your mind around a future where huge parts of Texas are changed forever.