I'm adapting the "Indicators of Warming" infographic into a shirt design and thought many of those NOAA indicators are a little egghead for a lay audience so I'm simplifying the graphic (as well as using my new 'flavor of the month' font and grunging up the edges which seems to suit shirt design):

I'm going to hand this over to Wendy to give it a revamp (better to get a graphic designer rather than a physicist to do the graphic design work). But before I do, can anyone suggest other or better warming indicators? Preferably something that goes with a good image - something that's tangible and visible that a layperson can easily conceptualise?

one might consider changing the 'rising sea level' to 'vanishing beaches', just because the 3mm/year value isn't quite alarming ('yeah that's like 30 cm/century, hah'), as this may occur due extreme weather events too.

on the same tone 'increased humidity' might be changed to 'when it rains it pours', 'shifting seasons' to 'altered seasons'.

I really don't like the 'migrating species' thing as species do migrate naturally, 'altered distributions' would be more accurate, 'rescheduled procreation' on some species but this isn't universal. 

'Tree lines shifting', as well as other plant species could also be 'Gardening zones moving'

Gotta stop here the second thunderstorm of the summer is coming close by.

Storm tracks shifting and hadley cell expanding? :)

Not sure about "falling" snow cover - I think it's a bit misleading as snow does fall, doesn't it? How about "decreasing" or "diminishing" or "declining"?

Sorry Ari but somehow Hadley Cells and T-Shirt don't quite go together. Unless of course this is a T Shirt for Meteorology Students. Something like

'Signs of Global Warming - Hadley Cells Expanding. For more facts Ask Here ^' with an arrow pointing up to the wearer

Not a T Shirt for ther masses but maybe for the in-crowd. Encouraging Met' students to get active is a worthwhile side mission.

More generally, various T-Shirt logo's that can be cool, in, and sticking it to the skeptics indirectly. Then license anyone who wants to to use the logo's. I know the idea of all this creative output being given away for free sucks but such is life.

Maybe a Sperm Whale & Giant Squid down in the dark saying 'Getting a bit warm down here ain't it.?' Funny, cool and aimed at getting people thinking outside their 'zone'

Image suggestion: A birdnest with crying fledgelings surrounded by flying butterflies on a leafless tree with a sign "store's closed".

for a T-shirt.

Agree with Baerbel on changing to 'decreasing snow cover'.  Otherwise it's good, I think you hit all the big ones.

"Decreasing" is a long word. Use "less" instead.

Sure, "less" works well.

"Vanishing cryosphere" would take care of sea ice, ice sheets, glaciers, snow cover and permafrost with just two words. :)

the average person reading a T-shirt may not know what the "cyrosphere" is.

You might want to add something like "more crazy weather" with a tornado, a flood or a drought icon.

Might make sense to have this on the front & back of a t-shirt. Following on from others suggestions:

- "heavier downpours"

- "bigger droughts" - perhaps too confusing for the masses.

Polar bears sitting on tiny ice floes...

I would advise against using tornadoes as an example.  More extremes perhaps?

"the average person reading a T-shirt may not know wha the "cyrosphere" is."

Well, we could make a zoomed-in image of dictionary entry of cryosphere below the text. ;)

And at any case, having a T-shirt with just text "vanishing cryosphere" would be nicely enigmatic.

the invasion of the jellyfish!

How many T-shirts featuring a "Portugese Man O War" have ever been produced?

People wearing T shirts in the winter?

Not directly ideal to put on a tshirt, but the site http://climatesignals.org/ gives often striking examples of direct consequences of GW and hence some inspiration...

BTW my comment wasn't about t-shirt design, but about an indicator.

You could have a picture of someone wearing the proposed T shirt (no other top)  and some text saying 'wearing a T Shirt in winter'.

Then on that T-shirt in the image would be someone wearing the proposed t-shirt....

Then on that T-shirt in the image, on the T-shirt in the image would be someone wearing the proposed t-shirt....